How can i get into shape for the army?

[Evan]

About four months ago, i had duodenal ulcers. during that time i wasnt doing much physical activities and i vomited just about everything i ate. Unlike what someone had told me last time i asked this question, this does not disqualify me from entering the military be it that i do not currently have ulcers, I am not sick, i feel fine. Its just i need to start gaining muscle, because i lost what little i had when i was sick. I havent signed up for anything yet, but i am completly sure this is what i want to do and im willing to take the time and effort to get into shape. now that i explained all of this, what would be the best, and fastest way to get into shape