Creatures 3 can be a fairly intimidating game to play for a lot of people, even those aware of its complexity. Here is a very simple guide that goes over some of the basic caveats of the game and explains some of the most basic elements. I hope this helps!

The Hand
This little disembodied hand is how you interact with the world. You have free reign to go about the Ark and interact with almost anything. Use the left mouse button to push something and use the right mouse button to grab something. Once you gain the ability (or have Docking Station installed) you can pick up your creatures by holding down Shift and clicking the right mouse button. You can also pet your creatures to reward good behavior and spank them to discourage bad behavior. Finally, you can even speak to your creatures! Just start typing and you can put in a simple command or teach new words to your creatures.

The UI
In the upper left corner of the screen is a little box which indicates what creature you have selected (if any), if you lose track of the creature click on their face in the box to get to them. There is also a hand and question mark, the hand will usually be the one brightened up but you can click on the question mark and then left click on something in the game to find out what it is (and teach whatever norns nearby a new word) or right click on it for a detailed analysis. This is an excellent way to find out how objects work and learn more about the lore of the world. You can also right click creatures with the question mark to get their bios and name them. To go back to the hand, simply click on it in the upper left box.
On the right side of the screen are three tabs: the top tab will list all creatures you have on the ark right now and you can click on their face to go right to them, The middle tab is the options tab which you can use to turn off music and sound, get help, pause the game, quit the game, and even name yourself. The bottom is your inventory, you can put objects and animals in here to carry to another part of the ark.
On top of the screen will be various circles with distinct symbols in them, these are shortcut buttons you can use to go straight to specific areas of the Ark and the Docking Station. You will need to go to each first area to get the shortcut.

The Creatures
* Norn: Adorable and incredibly stupid, norns are the stars of the show and the main creature you will care for. They come in a variety of species and have various personalities. Gog also includes some special species you could have downloaded from the Creatures website.
Just like other animals norns can also breed with one another, males can impregnate females after doing a G-rated mating ritual known as “Kisspopping” and later the female will lay an egg. If you don't want to bother with that though, there is also a big machine in the Norn home that you can use to create and even hatch eggs. Keep in mind that there is a hard limit on the amount of creatures you can have on the Ark, if you reach it neither norns nor the machine can make eggs.

* Ettin: Eccentric and strange critters who were made to run the Ark, but have a bad case of Kleptomania. They will wander around the Ark and steal gadgets to take back to their home in the desert terrarium. They can be quite annoying, but ettins aren't malicious and will play nice with the norns. All ettins are female unless you mess with their genetics with the gene splicer.

* Grendel: Big, mean, and green, grendels are the natural enemies of norns and will attack them on sight if given the chance. They will also carry diseases with them wherever they go. That said, with a lot of effort you can make grendels into gentle giants who like norns! It sure isn't easy though. All grendels are male unless you mess with their genetics with the gene splicer.

Both ettins and grendels aren't treated as pets initially unless you have Docking Station. If you want to make them pets and don't have Docking Station, check below.

Power-Ups
Throughout the Ark you will find unusual little blue rectangles with symbols in them, these are power-ups. Also known as keys, these special items will give you unique powers and upgrade different machines on the Ark. The bad news is you can't interact with them, the good news is your norns can and if you can get them to push or grab them you will get their power!
Alongside various machine upgrades you will find two special power-ups.
In the far upper right corner of the Jungle Terrarium is the Grendel and Ettein Selector power-up, get this and you can make grendels and ettins your pets just like the norns! Make sure whatever norn you send in there gets the power-up quick or they may get sick.
At the bottom of the elevator in the Marine Terrarium you will find the Grab power-up, this will let you pick up your creatures by holding shift and using the right mouse button. It is even MORE dangerous though given it is underwater, bring the elevator up quick if the norn takes too long or they will drown!
Note: If you have Docking Station installed, all the power-ups are given to you from the start. In that case you don't have to worry about putting your norns in danger to get them

The Ark
The Ark is a big spaceship made by the enigmatic aliens known as the Shee. The Ark is divided up into 7 distinct areas: the peaceful Norn Terrarium, the Learning Room where you can teach norns all possible words, the dangerous Jungle Terrarium, the barren Desert Terrarium, the beautiful Marine Terrarium, the Bridge where you can treat diseases your norns may be afflicted with, and Engineering where you can make new gadgets and even gene splice your creatures.

The Docking Station
This was a free add-on released to connect to the Ark. The Docking Station itself is a much smaller ship known as the Capillata, but carries four distinct rooms: the Hub, the Norn Meso, the Comms Room, and the Workshop. Note that unless you have mods installed, the last two rooms cannot be used to their fullest due to utilizing an online service no longer provided.

Gadgets and Machines
Throughout the Ark you will find a variety of gadgets lying around from cannons, to scent emitters, to sensors, to things that just seem to defy explanation. I won't go into much detail since there are far better guides on making machines, but you can connect gadgets together to make mechanisms to get specific tasks done from defending your norns to tricking grendels. Always remember the handy question mark in the upper left of the screen, use that to find out more about each gadget.
Machines are big... Well, machines located around the Ark. They either control functions of the biomes they are in or can be used to make more gadgets. If you are without Docking Station, you will need to power some of these machines with bioenergy gotten by breaking down agents in the recycling machine located in the Norn Terrarium. If you do have Docking Station installed, then you have infinite bioenergy.

Nutrition
There are three major chemicals needed for norns to stay healthy: fat, protein, and starch. When a norn needs one of these they will tell you (or try to if they haven't learned to speak yet), you can also check yourself with help from the Medical Bayin in the Bridge or the HoverDoc in the Norn Meso. What substances contain these chemicals vary but as a rule of thumb: food usually contains fat, fruit usually contains protein, and seeds usually contain starch. Getting the right balance of chemicals gives creatures ADP, a special energy that sustains them.

Disease
Arguably one of the most stressful things in the game is when your norn starts sneezing, that means they are sick. Just like in real life diseases can range from harmful to harmless. In creatures they come in three types:
* Genetic: The least common of the diseases, but often really dangerous. On rare occasions a norn may die shortly after birth, which means they had a genetic disease. There is rarely anything you can do to prevent this, sometimes that is just how life is...

* Environment: Any disease caused directly from the world around them, this includes a norn starting to drown underwater, aging more quickly due to stress, and being burnt by hot temperatures. These are the easiest to cure and basically amount to just taking good care of your norns and keeping them out of danger.

* Poison: The most common diseases, this is when something specific enters your creature's bloodstream and makes them sick. All creatures have a chemical known as ATP that keeps them alive and is born from ADP. The most dangerous toxins destroy ATP directly and is most often gotten by a norn eating something they shouldn't, basically being food poisoning. Just like in real life Norns can also just get sick from bacteria in the air. Overall to cure Poison you will need to get to the Medical Bay and scan your creature to give them the proper cure. I won't go into too much detail here since there is a lot to talk about, but there are more in-depth guides online and if you have Docking Station the HoverDoc is a tremendous help.
Note: Ettin biology is the same as norns. Grendels meanwhile don't get Genetic or Poison sicknesses, though even they can't avoid Environmental sicknesses.

Again, this is all fairly simple information, but I hope this helps those having a hard time getting into the game.