When you go to the airport the first thing you have to do is the check-in. You can do it online using your mobile phone or at the desk. A ground hostess there is asking you your Ticket and Boarding Pass. They also ask you your personal document, ID Card.
If you have any luggage you have to put them on the tape.
Pay attention to the weight! If the suitcase is very heavy (more than 20 or 30kg) you will have to pay a surcharge.
If you want to be sure of the weight of your baggage, check online the travel companies conditions. Sometimes they are different depending on the companies.