Tires: tubeless tyres v/s tube tyres, tubeless tire, airtight seal

Question
How do tubeless tyres hold air?

Answer
In lay man's terms when a tubeless tire is constructed an Inner Liner is incorporated in the inside of the tire, in essence a tube built into the tire.  The bead flanges are designed to conform to the flange of the rim thus creating an airtight seal.

Brett