Most airlines allow you to check in online from 24 hours before scheduled flight departure. In this way, you are not only sure about your seat on the plane, but you also avoid long queues in the departure hall at the airport. In order to check in online, you need the booking reference of your flight reservation. This is a combination of 6 letters and numbers.
Online check-in with numerous airlines is possible here.
At the airport
Anyone who takes a short-haul flight has to be present at the airport 2 hours before scheduled flight departure. For a long-haul flight this is 3 hours. Keep your boarding pass with you at all times when passing through security.
There are strict regulations with regard to liquids and potential dangerous objects in hand luggage. For your own safety, every piece of hand luggage will be checked. Please keep in mind that waiting time at security can be long and respect the regulations if you want to avoid extending it.
Respect airline baggage restrictions. If not, you risk paying a serious surcharge.
Here you can find the EU Air Safety List, which includes all airlines that are restricted from operating in the European Union.