This is not a dumb question, not at all. All calorie counters deal with this issue at least once in their weight loss journey.
I often answer but I usually forget one of the basics. "Eat less, move more".
There's a wonderful site called fitday.com. It's free. If you can figure out how much you have been eating in order to get to 218, all you have to do is cut. For instance if you are eating 2700 calories and staying 218, then theoreticly if you cut 500 cals each day (total 3500 per week) you'll lose one pound. So your goal would be 2200 cals.
There's also the "rough idea" which is my favourite. Multiply your ideal weight by 13 ... 130 lbs x 13 = 1690 cals per day.
There are also calculators and things on the internet but you are going to find that it's mostly trial and error. You can start low and find that you are weak and tired and so have to raise the amount. You can start too high and find you're not losing. You'll have to tweak as you go.
Exercise usage adds another element of confusion. That might be better discussed later
Ask more questions. And Welcome!