oh right, i thought you were trying to unlock apprentice in arcade mode with vader
hmm theres a lot to say about sc but i guess the best way to describe it is that it is like several giant rock, paper, scissors games going on at once.
so i figured you already know the hit properties as you played tekken, but in short:
high attacks - must be blocked high. can be ducked
mid attacks - must be blocked high. hits people crouching
low attacks - must be blocked low. can be jumped
then you got your A, B and K...
horizontal attacks (A) - hits people who side step
vertical attacks (B) - hits people who are charging in on you
kicks (K) - a bit random, genereally short range and fast
you need to find a character that you're comfortable with and suits the way you play and think, do you like range? speed? power? evasion? throws? etc.
learn what moves your character has, you need to find a good selection of moves for different situations and know what to use them eg:
- a few combo strings, maybe some that have a hit somewhere you can vary like a high/low hit. these are just some stuff you can attack with
- general really quick hits that you can throw out at random to stop people dead in their tracks, this is called a poke
- moves that stun people... once people are stunned its your opportunity to start a combo. you will need to learn or make up combos of course

- a very fast attack of some sort to use when you are getting barraged with attacks, generally used after their move/string ends or after you block to stop their rhythm or just so you can start attacking yourself.
- a fast attack to use after you block a slow attack with long recovery. this is called punishment
- a good strong hit to use when the opponent misses and is wide open. this is called whiff punishment. (whiff means to miss)
- learn which moves ring out. check throws too
this could go on for a while but thats a generic list with the basic situaltions covered. knowing the moves is just scraping the surface, its about knowing what a move is good for and being able to do it when the time arises
also if you are getting hit its best that you block. very few characters are fast enough to attack back whilst they're getting hit but nearly everyone in the game is capable of retaliating after a blocked attack (the slowest of characters will benefit a lot from guard impacts)
other than that just play the game (against humans, AI is a different game!), you'll see what works and what doesn't. also remember that nothing is cheap... if its in the game its there to be used. throws are not cheap, ring outs are not cheap, repeated moves are not cheap. there is a counter for everything.
i reckon thats the basics covered, i think ive written too much already >.<