Most are made of butyl rubber; lightweight tubes may use latex.
Valve Types.
Presta valves are narrow, used on road and performance bikes.
Schrader (or Auto) valves are larger (like car tyres) and used on hybrid bikes, mountain bikes and kids' bikes. These can be described as AV valves too.
Sizes.
Bike tubes come in different diameters and widths (e.g. 700x25–32c, 27.5x2.1–2.4”) to match the tyre.
The first number is the diameter following by the tyre width range the tube will suit. In the example above, these bike tubes will suit a tyre width of 25 to 32mm and 2.1 inches to 2.4 inches, respectively.
The "C" in a tyre size like 700×32c is a historical designation. It refers to an old French sizing system. It's legacy label that tells you it fits standard 700c wheels.
The "C" no longer corresponds to a measurable feature. It simply indicates that the tyre uses a 622mm bead seat diameter ( or internal diameter).