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E-ticket just means electronic ticket. Instead of a paper ticket to lose, forget, etc, it's all stored in their system now. I'm not sure many travel agent shops are actually giving out paper tickets now, so there is probably no difference in what you have and what you would get someplace else.

First and middle names lumped together is common, don't worry about it as long as the names are correct.

Please reconfirm 72 hours before the flight means you should call the airline and tell them you are reconfirming the flights. That's not very common anymore, it's possible they have been adding that to the receipts for years, but you just call the airline and they will tell you if you need to do it or not. Most people no longer confirm flights.

They do not say that you MUST check in online 24 hours before the flight, but they say that if you want to check in online you CAN from 24 hours before the flight to 90 minutes before the flight. If you don't want to check in online, you can also check in at the airport.

To check in online, go to the website, click the tab for checkin, put in your first and last name, and either the PNR record from the e-ticket or the e-ticket number and click continue, it will take you through the steps, and you can print your boarding passes if it's a flight you don't have to get them at the airport.

All it tells turkish is that you have checked in for your flight, not much more. It depends on the actual flights if you need to still stop at the airport desk or not, they may need to check for visas, etc

To review your ticket, you put in the ticket number and your name, not the person who paid for the ticket.

Some airlines will ask for the card used to purchase the tickets, but some won't. Some that do ask, don't need to see it if you did not buy the ticket directly from them. You need to check with Turkish to see for sure, but if you have the card and it's in your name you should bring it just in case. If it's not in your name, you need to ask them if there's anything else they need. They will know the flight was paid in full, they just want to make sure you are not using somebody's card illegally.

Nothing will happen if you don't check in 24 hours before the flight. Look at the airline website for the deadline to check in at the counter, it's probably 2 hours or 90 minutes or something like that. If you miss that deadline, they may cancel your tickets or give your seats up. There is no requirement to checkin 24 hours before.