Make sure you arrive at Seattle Tacoma airport (SEA) at least 3 hours before the flight if it is an international flight or 2 if it is a domestic one.
Check the luggage limits
(size, weight, items forbidden, etc) with your airline.
Have all the documentation to carry out the check in (ticket, passport, Visa).
available towards the Seattle Tacoma airport (SEA) and the Terminal where you depart. If you arrive at the airport by car check the airport
Check the Facilities and Lounges
(if there are) within the airport grounds, to organize your waiting.
Once inside the terminal, look at the electronic screens to know the status of your flight. If necessary, declare your new electronic devices at the Tax office.
At the check-in desk (if necessary) you can check the big baggage, show your ticket (printed or in your phone) and passport and receive your boarding pass. In case you do not need to check a luggage, some airports have self-service check in kiosks where you can get and print your boardking pass.
Then, at the security control area, if you bring a laptop or a similar device, in you cabin luggage, you will have to place it outside the hang bag. After passing the security area you will get in at the boarding zone. Check you boarding gate and wait the airline call, always having in hand your passport and boarding pass.
If you are a handicapped passenger, you should coordinate your trip with your airline at least 48 hours in advance and check the
facilities. Enjoy your flight!