How how how!?
P.S.::I want to know in the most simplest ways.
Ok, your ganna need a program called notepad :D
look, this is one of Raven's arena files:
{
map "mp/ffa3"
longname "Tatooine City"
bots "Luke"
fraglimit 10
type "ffa team"
}
Copy it, and add your map specifications. You need the exact map directory path. The longname is what appears in the menu. I dont think the bots or fraglimit matters. For type, you put what game types it is for (ffa team duel ctf... etc. etc...)
save it as your_map.arena then check the file and make sure the name isnt your_map.arena.txt it has to be your_map.arena