I dun understan some aayat of surah an nisa :/ Ramadan.?

The captives are taught islam and they leave in the islamic community some of them willingly accept to become muslims once they are muslims , a female muslim captive is forbidden for her unbelieving husband but she is pure for a muslim man to marry. The man who marries her would seek her husband and pay him the money he has spent on her. As for the slaves they have been sold and cannot return home expect their owners set them free but some slaves were brought from such far places at such tender age that they can't return even when set free and need i add that some people marry women at such tender age like 12years. As for the part u said u made mistakes ALLAH is oft forgiving most merciful so long as when u make mistakes u ask for HIS forgives then don't despair about HIS mercy. Whoever thinks u're a bad person because u made some mistakes his/her thinking has no effect on your deeds is ALLAH that u have to account to and HE is most forgiving most merciful.