What Installation Source to Use?

I began installation from the boot iso. I'm sure there are secondary locations on the web where I can find addresses for this menu (google),

but I'm confused why no standard installation source or repositories are included here or automatically configured.

Where would be the first obvious place assuming you were working with a boot CD and didnt know repository addresses off the top of your head? There is nothing in any of the guides.

Should I just copy the link from the dvd iso or what?