I believe you need to create some .arena script files to get it to show up in the skirmish menu of openarena, but if you just want to get the maps loaded and are freindly with the cosole then use
/map <mapname>
then set it up anyway you like. for example FFA with 2 bots
/g_gametype 0
/addbot sarge 2
/addbot gargoyle 2
/timelimit 5
/fraglimit 35
/map_restart (only really needed if your swapping out the game type)
for g_gametype modes are as follows, running from memory here so please dont hold me to it exactly as written, and of course correct me if wrong
.
0 - FFA
2 - TDM
3 - 1v1
4 - CTF
After that if you want to make various modes with map rotations then I'd suggest hit up the openarena wiki and create yourself a listen server config, then once ingame load said config with
/exec filename
to see everything you can do with console check this out
http://quake2.ukrpack.net/FAQ/con_commands_q3.shtmlmost of these commands will work with openarena's engine.