You mean future war cult? Well you have to pledge allegiance to that faction dude, and then some of your rep will go towards FWC. But I would not buy any of that shit because, again, its pretty useless if you can get blue and purple drops from just playing the game that are better.
As far as infusing if you open up the weapon/armor perks (purple or better) there is an icon on the left with yellow on it, so if you have the marks and the mats you can infuse a higher attack/def item to it to raise its atk/def. You can use purples as well as blues for the infusion. So lets say you got a nice purple gun that you really like but its only 220 attack, then you find a blue one with 250 attack later, you can infuse the blue 250 gun to make yours about 240ish.