Everyone loves to level. The thrill of watching your warrior, mage, or rogue gain levels and earn new skills comes second only to slaying darkspawn in a heroic last stand.
Your companions also gain experience (XP) at roughly the same rate that you do. Don’t worry about the companions you leave back at Vigil’s Keep; they progress at the same rate as the rest of your party. If you leave Anders home at level 8, travel around on a few adventures, and return at level 12, he won’t still be stuck at level 8. He will most likely be level 12, or close to it.
Each class gains levels at the same rate and gains the same points to spend, although each class will spend those points very differently.
For every level you gain, you gain three attribute points and one talent point.
Mages and warriors get one skill point every three levels, while rogues get a skill point every two levels. You gain specialization points at levels 7, 14, and 22. Points are precious, so spend them wisely.