There is a good Sticky thread at the top of this forum that has a good beginner's guide to exercise: Fitness Fundamentals
In addition, another thread that may help is this one: Speech on dietay myths
. Exercise is incredibly important, but the vast majority of people who lost weight lost the vast majority of their weight by changing their diet, not by exercising off the pounds. Exercise can help create a caloric deficit (which means burning more calories than you eat), but most would agree it's not nearly as important as reducing the number of calories eaten to begin with. In other words, weight loss is dependent 80% diet, 20% exercise. (Rough estimate, but a useful rule of thumb).