What is it you don't know about this? You do it like anyone else, does, I suppose. Contact the jail and find out what their requirements are, and find a justice of the peace... The jail or prison probably sees this a lot and will likely be able to direct you to a Justice of the peace to have a civil ceremony or just an "on record" marriage. But second question that occurs to me is why would you want to commit your life to a person who has shown themselves not to honor their responsibilities? Chances are he won't be different with you. Why would you want to set yourself up for that? He may be a good person and you may want to see the good in him, but sounds like if he is in jail that he doesn't know how to do that yet. Don't kid yourself that you will be able to change that --- or "save" or "teach" or "change" him.
I wish you all the best. Best advice to take a minute to really think about what this decision will mean to you and those you love. All the best.
I wish you all the best. Best advice to take a minute to really think about what this decision will mean to you and those you love. All the best.