Pretty simple. Be sure you have a POC that is approved by the FAA and the airline you're flying. Call the health desk of the airline you'll fly to find out what their rules are for flying with 02, get the forms filled out by your doc and carry them with you. When you check in, expect them to ask questions about your POC and be prepared to show them the documents your doc signed. Your airline may ask you to sit in a window seat; United's rules say you don't have to if you don't use 02 for take off or landing. Other than that, and lots of airlines don't even do that, it's generally a piece of cake.