Healthy now doesn't mean healthy tomorrow, remember this. Obesity is a lifestyle, extreme obesity is an extreme lifestyle, being fit is a lifestyle. Changing lifestyles is either said than done, but with determination and building better habits, you can surely make such a change.
3 things: diet, weights, and cardio. Diet is the cornerstone to weight loss, I tend to think it is 70% of the ballgame if not more according to some people. Watching what you eat is almost more important than how much you eat, but if you hope to lose weight, you will have to reduce how muc you eat as well during that time.
Weight training helps you build muscle. The more muscular you are, the more calories your body will naturally burn.
Work your way up with cardio, it's fairly easy to get discouraged with cardio because it's hard to know how much to do. For you, I would say 20-30 minutes 3+ times a week. Again, work up to this gradually. This doesn't have to be running. If I decide to run for my cardio I do it at a pretty slow and steady pace. It takes time for endurance to build up, and can fluctate in the course of a year, so don't be discouraged by this.
Invest in a gym membership. Even on the high end say $400-$500 per year would really pay off in the longrun for the results you will be seeing. If you're in college (I know you're mentioned that you're 19), campus gyms are usually pretty well priced. The community college I went to had a great gym that I had NO trouble getting on equipment and I payed $260 per year. A gym membership isn't even necessary, but it is helpful to have access to everything.
My buddy Jerome went from almost 300 pounds in highschool, down to a lean 200 lbs 3 years later in college. When I say lean, I mean six pack lean.
I hope all of this information doesn't overwhelm you. It is important to work your way into in order to make it habit and a routine that you can fall in love with and do everyday. Good luck!