It's worth remembering that exercise is typically a fairly small part of your overall calorie burn. Most people burn between 1300 and 1900 calories a day just keeping their basic body functions (aka metabolism) ticking over.
Exactly how much to eat and exercise can get a little complex, as a lot depends on your personal circumstances. Fortunately, Spark takes care of all the math for you.
Just set up your target rate of weight loss, and your weekly Exercise Goals (both accessible from the LH side of the start page), and Spark will come up with an intake recommendation for you.
In terms of exercise, rather than coming up with an arbitary number of calories, I think it is easier to think of it in terms of time, and how much time you can commit to exercise on a regular basis. Most experts recommend 30 minutes 3 times per week as being consistent with good health, and perhaps increasing this to 4-6 times per week for weight loss. You can enter these figures into Spark's Exercise Goals, and Spark will convert this into an exercise and intake target.