If you've gained this much weight, you're obviously eating the wrong foods.

1) Cut out or limit refined carbs - this is sugar and white flour.  The less refined carbs you eat, the less fat (and other health problems) you will have.

2) Start a little exercise now, nothing too intense.  Walk a half hour a day, lift weights a couple times of week.  You should get the diet in order before you focus too much on exercise.