Lets say I have a t-shirt and I want to cut it and make holes in there.
How do I do that? Like delete polygons or something like that. Maybe theres a brush or technique.
Thanks 
You can use mask and extract to create ripped clothes.
Watch this:http://www.youtube.com/watch?v=-1b6UPa6DRo
Hmm…you can also mask off an area and hit delete hidden.
How about this:idea:
http://www.pixologic.com/docs/index.php/Joseph_Drust#Using_Surface_Noise_to_Generate_Clothing_Holes
James