"..Please Explain?"

Explain what? Why I shouldn't do your homework for you?

C'mon - do a bit of research. Make an effort to answer this yourself - or at least show some signs that you have. Ever heard of google? 2 minutes of googling should give you a wealth of information.

Cheers,
Darren :)

PS. If it's not homework, then I apologise in advance for my first remark, but the second remark stands