HaloMods "Classic" Read-only Archive

well i was looking around some stuff and i saw something called the killtrocity map pack now what i read was it had like alot of maps so you have to go and add every single one of those maps through the "grueling" process?

I'm new to the whole thing and I'm just wondering if you download maps from the site does it replace any default maps or does it add them as if there are 5 maps after u add the modded map you have 6.....