alright so im gonna make this really easy guide on how to add TF2 maps to your list just in case theres any n00bs out there that wanna know.

FIRST
your gonna want to find a map and a website i would recommend is fpsbanana which is a really good site for any steam/valve games to get skins, sprays, maps, and just about anything so ill be making more guides possibly for that.

1. Find the map, and i decided to use this map which is an engi acheivement map... so download it to your desktop or some folder where you can get to it.

2. now once you have the .zip downloaded you open it and ur gonna wanna go to the .bsp file and to go to your tf2 folder juuust....
go to your C Drive>Program Files (x86)>Steam>steamapps>[your steam username]>team fortress 2>tf>maps, and there you are. and this is where you add your maps , now you can go into local games and acheivement farm and whatnot or whatever you wanna do with the maps

Super Simple