For online game play you have to find a server that is running the mod.
For you to play by yourself, select "instant action" and on the top of that window are several tabs, game type, map, and I believe "mutator(s)".
I'm doing this from memory since I'm not on my home PC. Go to mutators and on the left-hand window find junk wars and add it so that
it shows up in the right-hand window.
Select the rest of your choices, gametype, map etc, if you haven't done it yet and click "play". Now you can mess around with the
weps.