Well when it comes to repeling energy, theres a few things you can do base on the circumstances. If someone just shoots a regular ki blast at you (a small energy ball, the primary function of the b button - very little damage), if you block at the right moment you can send it back at them.
If someone use a blast 1, or blast 2, you can energy block it, and stop it from doing max damage, or knocking you down. There are times however, where I have send a blast 1, 2, and even an ultimate blast at my enemy, and have had them shoot a blast 1 or 2 back, in which case the blasts collide, and you have to spin your joystick uber fast to get yours to win. Im not quite sure how to counter-blast yet though, i think you just have to do a blast before they full cast theirs.
Hope that answers your question