Diet will do more for slimming your body than exercise will. Cutting out processed, simple carbs (white rice, white sugar, all-purpose flour), soda, sweets and junk food, reducing fat, cutting calories/portion sizes will probably lead to huge changes in your body and obvious reductions in the amount of visible (and non-visible!) fat. These are simple steps to get started.
*Any* sort of exercise is good for getting started. Even walking a few miles a day, or as much as you can, is good. Power walking, running, biking, going to the gym and hitting up the elliptical/treadmills, biking, etc- all of these are great, but if you just want to start with walking that's a step in the right direction.
I'd check out the 'exercise' forum and some of the sticky threads at the top to get ideas on general exercises practices. Stumptuous.com is a great resource for at home-training.
For right now just to get started *any* sort of healthy change is good- again, cutting out low-nutrient/high fat/processed food (or at least cutting it way back), portion size, and starting to move more are great first steps. You don't need a very technical, complicated exercise/weight loss regimen to lose weight, especially at first, just some common sense choices