There are instructions on the seat back card.
However, you just connection to the flyfi wifi network it should auto send you to the sign in page where you put your name and email. You can connect for texting and using social media and email for free. If you need streaming video it will cost unless it is on
Amazon (which I think is free while you are flying).
If you can't connect just ask the flight attendants they are pretty good and showing you how to do it.