You have a lot to do and it involves a word that you will shortly hate. That word is "Saddle" and what you have to get is "Saddle Time". Won't say every chance you get but as often as you can get the bike out on a local route and ride. Try to find a flat route direct from your house so it is easy to get to ride. if you can start on a 5 mile ride then good. If not- work up to a 5 mile ride.--Then each week just raise the mileage a bit to 10 miles. In other words- just ride.

It may hurt initially but back to that saddle. Sitting on a saddle will be painful. It may be the wrong saddle but you have to harden up the butt. Get the saddle and butt attuned to each other and it will be easier but until then you will experience the worst pain you think you have ever had and it is called "Butt Ache" Saddle time will improve the situation and by the time the Butt ache has stopped- you may be up to sensible mileage on your rides.

That is your first stage so what are you doing reading this. Get the bike out and ride---NOW.