What is the best way to breed mollies?

I know that mollies are live bearers and give birth to young fry that are free swimming i also know that they keep giving birth even though there is no male but I'm wondering how long it takes and how many times they will and stuff like that i want to know everything. I got 3 mollies but the person didn't let me pick which ones i wanted so i ended up with 2 males and 1 female. will this be ok or should i just put the 1 male and female together? I have a 20 gallon tank with just a couple other fish in there. also is it ok if for breeding purposes to but them in a one gallon until the female is pregnant and then remove the male? these are things i wonder also if anyone can tell me can mollies change from a male to a female if there are not enough females? thanks for any help!