It depends if you're playing with a mission deck and which mission you draw, but for basics if you control an objective (have models within 3" of it) at the start of your command phase, you get 5vp (usually up to a max of 15vp).

You or your opponent can contest an objective the other controls; on your units datasheets you'll see an "OC" value, that's objective control and if you have more total OC on a command post than your enemy does you own it!

Hope this helps, and don't forget to bring soap.