First download the file.
2 use winzip and open the zipped file you just downloaded
3 find the file that has the map name with an extention of .pk3
4 hit the extract button and put it in your mohaa/main folder
I don't know if I really understand your question...but
If you are hosting a server you go to start game then select the level you want to play from the list. or type in the level.
I think thats what you meant.