With nexuiz closed, download the map to your data directory.
Then type "maps" in console and it will show a list of all of your maps.
Then type "map mapname" and it will load that map for you to play
If you aren't sure about the map name, then type "map " plus the first few characters of the map and press tab and it will auto-complete the mapname for you (or show you multiple files that match that pattern).
Loading a map this way will default to 5 minutes of gameplay, so type "timelimit 20" or whatever.
Type "bot_number 4" to add some bots to the map.
And for other settings to try, search by keyword here....
http://www.nexuizninjaz.com/toolz/cvar/
so if you want to know about bot settings, then search for keyword "bot".