An e ticket is just held on the airline computer and allows them to check you in based on some sort of ID. Often airlines ask you to bring a passport or similar to prove this.
Some will also issue you a booking reference that you can quote but if you know the flight number you are usually okay. Booking reference should also allow you to pull up any details on the airlines computer.
Return journey works the same, turn up and present yourself and ID.
The one thing to remember is to print the flight details then you know check in times etc.
Hope it helps.