Downloading them from the openarena.ws webpage.
Didn't know that we had maps there
I think it might be that you have navigated your way in to the SVN, which is not where you would find the maps as such.
By simply installing Open Arena in desired location you will have access to all the maps included in the package and ready for play, it automatically installs the maps in the correct location.
If you refer to third party maps (which are not officiall supported by Open Arena) you will need to locate these maps yourself and place them in your /baseoa directory. For instance take a look at
DO NOT LINK[/b]) h t t p s : / / openarena . wikia . com/wiki/Third_Party_Maps]Kinjada's List of working maps or the 100 map-pack I released as a
.torrent here.
Alternatively you can also 'enable' downloads in the game and simply connect to a server that runs any custom maps / mods, it will then download it automagically, but do this on your own risk. Good luck with it..