My flight was delayed for more then 3 hoursYou can claim compensation, if your flight was delayed, and you did arrive with more than 3 hours of delay at your destination airport. Only in extraordinary circumstances (very bad weather, strike) the airline does not need to pay.
My flight was overbooked, I was refused boardingIf you did had a valid flight ticket / boarding pass, but was refused boarding. Usually this happens if an airline "overbooks" a flight. That means they sell more tickets then seats available.
I missed the connecting flightIf you missed the connecting flight, because the 1st flight was delayed, and you did arrive at your destination airport with more then 3 hours delay.
My flight has been cancelled If your flight has been cancelled and the airline didn't inform you 14 days ahead, this is for you.