Well, step 1 is to re-lace and tension the rear wheel you partly took apart so that you can remove the freewheel. Use the other rear wheel as a guide to where the spokes go and how they cross, and roughly how much they should be tensioned. Don't worry about getting the rim true. Then purchase the appropriate freewheel tool and wrench and remove the freewheel. If you can accomplish that much without stripping nipples and mangling freewheel notches, that will demonstrate you have the mechanical aptitude to proceed to rebuilding your hubs and wheels and then move on to other bike maintenance.