Macbook Time Machine with an external hard drive?

I'm new to the time machine and external hard drive part of computing :) Basically I have an external hard drive that I just started using as my time machine. I need to know that after time machine is done with it's backup can I delete the files from my computer. Does time machine back up iphoto? If so, can I delete the pictures from iphoto after time machine is done? Thanks for all the help.