Mollies are common Livebearers. There are not a whole lot of things you need to know. They will just breed. You want to keep a ratio of 3:1 for females to males so the male doesn't harass just one fish the whole time.
Some tips that don't directly help breeding, but may lower stress for the fish, may also let your fish feel more comfortable to breed.
1. Clean, stable water. Do plenty of water changes in large percentages when in doubt. Read about Mollies
here.
2. Give them hiding places. Fake plants and rocks will block line of sight, giving fish a place they can escape to in case of danger. Be careful with rocks, as choosing rocks from outside may raise pH or add other harmful additives to your tank.
