I read that you could do force attacks using L2 + triangle, L2 + circle and L2 + X. I've been able to do the L2 + triangle but I can't do the L2 + circle and the L2 + X. Does anyone know how to use these force attacks?

you have to unlock them.
You get up to 3 "upgrades" at the end of each level depending on how you score.
And in order to get the 3 different powers you must score high enough on the 3 levels that offer those force powers as upgrades.
I think the "0" power is unlocked on Tatooine but I am not sure where the others are.
Think I made this too complicated....
Do real well on missions so that you gain the 3 upgrades at the end of each mission, and your bound to get the force powers.
Hope that helps some.