This makes you invulnerable to other players but also prevents you from using weapons or attacking, so it's best used when you're peacefully exploring and don't want to be interrupted. Starting out, a lot of stuff will be locked until you're a certain level.

Cash is necessary to buy new guns, clothes, and properties, while RP increases your overall level. It takes about an hour, but the tutorial, in which Lamar takes you on a few missions, is a vital introduction to different aspects of GTA Online.

They subtly affect what level your skills start at, but it won't matter in the long run. Aside from your appearance, don't sweat the choices in the character creator too much.