Could Anyone Explain Please

Hi,

I have a Canon 7D and a 430ex ii Speedlight, and I understand that I can fire the flash off camera remotely with with 7D pop up flash as the 430 is a slave. What I would like to know is if I was to buy a 580ex ii as well could I fire both of these off camera with the 7D pop up ? or how would it be done as I get confused with the Master and slave thing. I would appreciate a simple explanation of any sort as I'm new to off camera flash.

Thanks in advance
Don