I need a bit of assistance. I'm playing a mage but can't figure out how to set up my spells...anyone? Thanks in advance.

What do you mean exactly? You just right click on either the LMB/RMB or a hotkey to assign a spell to them and then use. those to cast the spell.

What I mean is how do I set it up? Or is the appropriate spell automatically assigned for use? What is LMB/RMB? Sorry if I seem a bit dense but I just want to make sure I get it right.

Okay, I'll try to make this as simple as I possibly can. How do I make spells available for each mouse button??

In the GUI near the bottom of the screen there are buttons labeled with 'L' (for left mouse button) and 'R' (right mouse button). If you right-click on one of these you get a popup where you can select an action. Note that the potential actions for 'L' may be severly limited.

Also note that I am (unlike previous poster) not an expert at this game so I may be missing something.
Also note that using hotkeys may be better than mouse button - especially if you want to use more than one spell in combat.

I'm not an expert, either. That is why I asked. I wasn't able to find anything online so my only choice was to post the question here. Thanks, I really appreciate your input. :)

Basically put points in the mastery bar to reach the skills you want to use. Then put a point into a skill and assign it to the LMB/RMB/hot key so you can use it.

https://www.grimdawn.com/guide/character/character-basics/

Thanks, I finally came across that site. I think I'd do best to start over with a new character and give it another try. This is actually a much more complicated game than what Diablo 3 is.