to do this you need to download this map from google drive
just copy and paste this link in chrome, explorer, fire fox, etc. and download the file

https://drive.google.com/open?id=1DPBblA-XXAtUpExLNJbmOs2iKf7cX_Mf

once you have the map you want to add, right click on it and copy it. After that you have to go to the library, right click on the game`s name and left click on propieties, then on local files and finaly on browse local files. ones u are un the game files select "maps" folder and paste there the map.

You have to restart the game for it to work.

Now that we`ve added the map to the game is time to use it
1) go to host
set mode to ctf
set time limit to 0
set score limit to 0
2) go to map list and select the map (granja xp.bmap)
3) return to host
4) go to server options
set max players to 20
set spawn time to 0
set grace period to 0
set bot difficulty to easy
set bot team to blue
<go to more server options>
set autobalance to off
5) return to host
set bots to 19
6) go to mutators
set max life to 1
set infinit ammo to on
<go to more mutators>
set rocket madness to on

RECOMENDATION:
If your pc isn`t the best you should set video options as fast as posible and don`t go to bot spawn,

IN THE MAP
once you are playing in the map you just shot to the bot`s spawn. If you have lost your account use the assault rifle. The best option is to use the acid gun