Tubular tires just look the same as clinchers outside, but work in a different way. Tubulars are totally round, and there is no open part of the tire where needs to clinch.  There is also no tube needed as the tube is basically sewn into the tire and is part of it.  The tubular is just one piece, but the clincher is two pieces (tube and tire).  Tubular tires are always  glued to the rim, because without some glue they will move around a bit.

Tubulars are not common as clincher, but always popular in many road and triathlon cyclists.  They tend to be lighter and sometimes more durable.  If you are not used to working with tubulars, though, it may take a little practice to become handy with them.