usually with rts campaigns restrict you from straight building everything right away. you have to progressively "unlock" capabilities of building advanced buildings/units until a certain part of the campaign is reached. what i usually do is hit 'skirmish' (usually what the single player vs. computer is called) and see what you can do..then hit multi. rts isn't as forgiving in multi as fps, i'd be pretty impressed to see someone do well against someone who has been playing for some time when they just start with no idea how things work or what requires what. but once you see everything through a couple times then do multi, you at least have a basis to start with. i've never played ra3, but this is pretty much how every rts i've ever played went down...could be different.
