Follow these instructions to meet your goal:
1st) Join two or three other people to make your team.
2nd) Decide who is doing what part of the process:
a) definition
http://en.wikipedia.org/wiki/Street_art
b)techniques
http://en.wikipedia.org/wiki/Street_art#Techniques
c) history of graffiti
http://en.wikipedia.org/wiki/Graffiti
http://www.valladolidwebmusical.org/graffiti/historia/02prologo.html
d) editor
3rd) Use the resources to find useful information on the net. Select the most important parts and summarize them.
4th)Put all the information together and edit your text. Don't forget to include some pictures.