While we don't recommend that those looking to lose weight or get in shape need to count calories (if you are eating 2-3 meals per day that do not include crap or booze, then you really don't need to count calories!). HOWEVER, not all of us have it so easy, and for some us, counting calories makes us feel accountable for our progress. It's the same thing a keeping track of workouts.
But before you can start counting calories, you need to know how many calories you should be eating per day. You can figure out how many calories should be eating if you want to lose weight by multiplying it by 10 or 12. It's also important to know that the body wasn't built to have the exact same number of calories every single day. You should stick within a range.
Here is a calculator to help you as well: