*I am new to server-side scripting and have little to no knowledge of how servers are set up.*

I am trying to learn PHP with an Apache server. Do I have to disable IIS for Apache to run(localhost stopped working when I did)? Where do I need to save my php files for my server to process them? Finally, I may have accidentally set a password for my server (so I get prompted when I try to access localhost; how can I change this?