When you capture a plex, the militia will award you with Loyalty Points. Offensive plexing (capturing plexes controlled by the enemy) pay out more than defensive plexing(defending your faction’s plex). To join FW, you’ll need to join a militia. You can do this solo, in a corp or in an alliance. If you’re Gallente, you can try out these guys
Gallente and Minmatar are allied so I think you can fight for Minmatar even if you join them but I would be more convenient to join a Minmatar corp. Also noone lives underground so don’t keep a ear to the ground:). Pretty sure these guys do FW too.