can someone give me some vids on how to do thumb grinds i was think of doing them
here are some good vids,
or this
you just simply put your thumb into the inner/outer grind ring. Your thumb should be in a slanted angle, try watching the vid to clear it up 
Try tilting the yoyo, it helps.
Thumb Grind transfer:
Thumb Grind:
Happy Throwing! =]