If you've ever played any of the Call of Duty games then you should be familiar with the basic controls and HUD, but there are a few small changes especially on the Xbox 360 version as it is the first Call of Duty to appear on the platform. For newcombers to the series the controls aren't particularly easy to pick up but the main basics will be explained to you in the Red Army Training mission in Moscow, that being the first mission in the Campaign mode.
The storyline of the game is totally new and so therefore doesn't follow on from Call of Duty 1 or it's expansion. Characters too are new and don't really need to be remembered although soldiers are your own squad will have their name in green when you point the crosshair over them. Anyone without a name is an enemy.
In the first few missions it is hard to distinguish troops, especially the Russian and German troops who both wear grey. But you should soon be able to distinguish and using the compass should help to. If you do shoot a member of you team then you'll have to restart from the last checkpoint. Also try not to hold down the right analogue stick as that is melee attack and if you melee attack an ally then you'll also have to restart from the last checkpoint.