Checking in at the airport is often possible from 4 hours up to 2 hours prior to departure. The information screens at the airport show which check in desk belongs to your flight. You will receive your boarding pass at the check in desk. Here you might also drop off your baggage.
NOTE: some (low-cost) airlines might charge extra fees for checking in at the airport. Please contact the (website of the) airline directly in case of any questions.