Can a person who is using O2 board a plane?

No.

A person who is on oxygen cannot bring their own oxygen onto the plane. He can bring it into the terminal, but not onto the plane.

If a person requires oxygen during the flight, the airline furnishes the oxygen, but you have to pay the airline an additional amount over the ticket price to furnish it.

You need to call the airline to make arrangements for any in-flight oxygen required.

When the destination is reached, the person requiring the oxygen would have had to have made arrangements for someone to meet him in the terminal, at his gate, with the oxygen he requires.

Usually whatever company furnishes him with his oxygen will perform this task for a fee.

Yes and no. It has to be a specific model of O2 unit and have to check each airline as they are all different in their policy. See http://www.homeoxygen.org/airtrav.html