I think I need help.

Well... But are you talking about Tekken 5 or Tekken DR? If you have a game in your home, then it's good to make some practice.

The combos you might want to practice are here:
http://manjikai.com/yts/forums.php?m=posts&q=13 (see somewhere in the middle)

Also, go to match movies and upload some Qdogg versus Souten fights... by watching them, there's a lot to learn... If you have any specific questions, feel free to ask.

My top Yoshi's moves:
SS+1, FC,D/F+1, d/f+2, D/B+2,2,2,2, d/f+1,1, u/f+3, f+3+4, d/f+4, d/b+1+2~1, u+1+2+extensions. BTW, throws are also good :)

cheers :)