Well I'm probs best to help you on this as i am known to be a bit of a fifa legend...
A - Pass. This makes your standard pass
B - Shoot. Makes your shot but be weary of power bar as holding to long will overpower nd make it look like your playing rugby
X - Cross/Chipped Pass/. Generally a chip pass but if your on wing near 18 yard bow it will cross it
Y - Through Pass. Use this to play forward balls for your players who are making a run
LB+A - Pass + Move. Same as before but the player who makes the pass will now make a forward run
LB+B - Chip Shot. If your 1 on 1 and keeper comes rushing use this to chip over rather than trying to curl around him
LB+X - Early Chip Pass/Cross. Same as Chip but early like if your on wing but not at box hold LB+x and will play an early cross rather than you having to run up to wing first
LB+Y - Chipped Through Pass. Same as other but it chips the ball instead.
RT- Sprint (hold). I think you get the general idea on this one? haha
LT - Skill moves. Hold down LT and use the right analogue stick in diff combo's to do diff skill moves
RB - Finesse. Use this while taking shots (hold) and rather than you lacing the shot the player while place it.
A- Standing Tackle. Hold this to get your defending player to move toward ball holder and do a standing tackle
B- Call On Help. Holding this will call for another player to come to your aid and tackle ball holder
X- Slide Tackle. When near ball holder press this and player will slide tackle but time it right or you will give away a freekick
Y- Rush Keeper (hold). NEVER USE THIS! Only reason you should use this button is if their player has got past your defenders and is 1 on 1....use very wisely though as they could chip shot or go around your keeper and still score
LT+A - Contain. Holding these will make your defender rush to ball holder and apply pressure. he will stay bout 3 foot away from him at all times which makes it harder for opponent to do much like pass/cross/shoot as your guy will be between him and the goal
This best bloody help you alot as it's taken me bloody ages to write it!! haha.......Also if you get Fifa 12 im gonna kill you as the buttons are different! haha x