Broker have 2 category..
1st: Straight through processing...
their gain thru spread currency by liquidity provider offer and
comission by post u trade..
2nd: Market Maker (we call bucket shop)
their gain when u lose trade..
This is one of STP broker i used... U can learn more about
forex using automatic copytrade system. just follow the best
trader: www.mocazfm.com