How do classes work on battlefield 3?

I just got battlefield for xbox and it is confusing me a lot. In one game it will have the m16 for the assault class and another game it will have the ak74m. The guns for each class always change every game and I cant figure out how to customize them either.How do classes work on battlefield 3?
The starting rifle for the Americans is the M16A3, and the starting rifle for the Russians is the AK74M. Once you unlock another gun you can use it on either faction.



Press X/Square to edit the class.How do classes work on battlefield 3?
There's 2 sides, they change every match (if you don't exit the lobby) let's say like Russians, and Americans, You'll get american weapons once, then after the match is done, you switch to a different side. (Only 2) and that should also solve the custom class problem.How do classes work on battlefield 3?
If ur on the US side you'll get American guns. If your on the other side then you'll get diffident guns. How ever this only happens with the default guns. Unlock more guns to be able to use it for both sides. And press X to customize
If you're on the US team you get a M16. Russians don't use m16's they use AK's