Hi, here's a tut on how to do graffiti like this:
First, start of with almost any texture you want, i'm gonna use this brick wall:
After you chosen your texture you need a font, there are many free fonts on dafont.com i'm using this one:
Write your text on a new layer:
Use paint bucket to fill the empty spaces of the text with colors (if your font doesnt have empty spaces you can just color the whole letters):
Now you need some "dripping" lines to make it look more realistic, use