The tuba is the largest and the lowest pitched brass instrument. They are made in 4 different pitches and range from 12-18ft long. The tubas made to sit on a person's lap are known as concert tubas or simply tubas. the tubas that wrap around a person's body are known as Sousaphones, named after John Phillip Sousa.
Tubas have either piston valves or rotary valves and range from either 3-6 valves. Most sousaphones have 3 valves.
Here is one of my favorite pieces...Gustav Holst Suite in F. ENJOY :)