Sorry to take a while to respond (thanks for the assist jespah
Jespah is right, I'll just add a bit more.
First things first, a few things to keep in mind:
You need to set achievable goals, set your self up to succeed.
You might never be a big, buff body builder,..you need to accept the limits of your body. That's not to say you can't look and feel great, which IS the goal here.
Are you planning on working out at home, or are you going to a gym?
Most gyms are pretty affordable now, I know here in Boston, you can join a decent gym for about $20.00 a month.
Most of these places have personal trainers on staff, they're there to help, and can help you get started, as well as gain a better understanding of what YOU need to do to accomplish your goals.
Warming up is necessary for all forms of exercise, it's important to raise your body's core temperature, and get your joints and muscles ready for the workout.
Cardiovascular exercise is required for good health, and balance in your workouts. If your trying to gain mass, you may be advised to limit this to the healthy minimum.
One of the most effective ways to workout is what they call "circuit-training", which is a combination of high speed weightlifting exercises, where you move quickly from muscle group to muscle group in timed sets,...it gives you the benefit of weight training as well as cardiovasular work. It's a time saver, and the results come faster. It is designed to give you a leaner look, not so much bulky but muscular and well defined.
It's also more difficult, but it is very effective.
Cooling down/stretching is one of the most important parts of the whole thing. It helps increase your flexibility, and helps your muscles to relax and begin healing faster.
Carbohydrates are foods that break down to sugar quickly, helping to give you energy faster, they include breads and starches, grains, fruits and vegetables.
Proteins are foods that take the body longer to break down, have valuable amino acids and enzymes that the body needs to build with,..these are your meats, fish, dairy, nuts and, yes, tofu.
Your diet will depend on the exercise program you choose, I wish I could just tell you what to do, but it doesn't work that way. I can give you some general information, but you really need to see someone to put you on the right track for your body type.
My best guess, if you are really motivated, is that you'll need to workout 4-5 days a week, for an hour to an hour and a half per session.
You'll start to feel a difference immediately, and start to see good results in about six weeks. Don't be impatient, it took your body 19 years to get where it is right now, it'll take a little time to make the changes you want to.
Hope this helps, my brain hurts now