Right now, you are going to be doing Base training.
Because you are just starting, you need to spend some time laying down a fitness base. You do that with long rides that are easy, or moderate in effort. Seriously.
Ideally, you should have a cycling coach. Failing that, you could try one of those credit card coaches like CTS But I can get you into base training for a buck or two.
call Bicycling Mag, ask fro a reprint of "The Best Training Plan...Period" Feb 1994 pg 69. It's a classic Base training program. Do the advanced version, and prepare to suffer.
After a couple months of that you need to get evaluated by someone who knows what they're doing. This should be in person, so they can check the little stuff like riding position. They can also set you up on a program that will move you into the next phase of training.