Pretty much just started the game. Found shady sands, found this abandoned shack housing vault 15. I click on this hole expecting to be able to climb down, nothing. I just walk over it. I stole some rope in shady sands and figured maybe I need that to climb down, tried to use it, not possible. Is there some mouse/button command used to climb down things I just don't know about? Or Is there something else I'm supposed to do first before entering vault 15? I've wandered all around the map and haven't found anything else of significance i can do yet(except die a LOT cuz I'm barley level 2). Thought I remember the overseer at opening of game saying to start with vault 15 when it comes to my quest for the water chip.

Also, on an unrelated note, is there a certain way to go about interacting with NPCs? When I'm in a town ALL I get is "hellos" and "nice to see yous"? I was expecting deeper, more interesting interactions/dialog exchanges. I also came across a merchant and his guards whilst wandering the wasteland. I figured merchant, maybe I can buy stuff/trade. But he wouldn't say a word to me. Ended up robbing him of like 85 caps and then went on my way. Am I supposed to do something in particular to talk to/engage them?

Have you looked in the hut? There should be a ladder going down.
The rope you will need to go down the not working elevators.

For the NPCs, forget most of them. The only use they have is for the atmosphere and
you can steel little money from them...oh, and if you want to go evil...kill them.
In the game there are only around 2 - 3 dozens NPCs you can *talk* with.

The merchant is one of the random encounters...and sometimes bugged.
And if there are some attacking animals the risk is high that after the fight
the guards will attack you.
Their only use is early in the game if you have many hides you can sell them.
Or just rob them like you did.

I imagine you've explored the right-click options, or barring a right-click, the power of the N and M keys? (While I don't so much assume you've done the latter, they replicate the functions of the former.)
As to NPCs being largely useless, while it's tempting to write them all off, 13 years after I started playing I only just discovered one of the Brotherhood of Steel is named Jennifer. Who is she? What does she have to say?

haha that was the problem. I figured it out fairly quickly after posting this, but it was the right click. Of course, right click. I feel quite dumb for not figuring it out at first. Chock it up to this being the first game I've played on PC in over a decade(well it and plants vs zombies).

I talk to pretty much everybody.

I didn't know you could get animal hides. I searched several rats early on after killin em and it never gave me anything I could take, so I never bothered to check again.

Hides? How do you mean?

Are you sure you didn't mix up Fallout and Fallout 2?

Afaik the only hides are the gecko skins in the second game.