Since
Weight change = Caloric input - caloric output
This means you can either raise/lower your input, or raise/lower your output. So for losing weight...
If you are aiming to lose weight, one rule of thumb is to create a deficit equal to 20% of your TDEE (similarly, 20% surplus for gaining weight).
So if your TDEE is 2000 calories, and you wanted to lose weight, you might consider a daily deficit of .2*2000 = 400 calories. This means you can either eat 400 fewer calories per day than you normally do, or exercise more such that you burn 400 extra calories per day. Most people do a combination of both.
A pound of fat is 3500 calories. So this means if you hold a 500-calorie deficit for a week, you lose a pound of fat. One general rule that gets thrown around a lot is that you should try not to lose more than 2 pounds a week (1000-calorie deficit/day) unless you have a very high bodyfat percentage (30%+), because by that point you are likely to lose lean mass (i.e. muscle) in addition to fat, rather than just fat as desired.
The more accurate way to gauge your caloric needs is through trial and error -- tracking your calories and weight and activity and seeing how your weight changes over time. From there you can either eat more/less or work out more as needed.