Your e-ticket/(flight) ticket contains all the information you need to check in (online) for your trip. You don't need to print your ticket, but make sure you save your ticket, so you can always find it. You use your ticket to check in online or at the airport.
With most airlines you can check in online from 24 hours before departure and with some airlines it is even mandatory. Check the airline you are traveling with or go directly to their website to check in online yourself. Although we recommend everyone to check in online, in most cases it is still possible to check in at the airport.