A cryo pump uses a cryogenic fluid that entraps the gas molecules inside the chamber and freezes them below their freezing point. A cryo pump doesn't work very well with gases like He or H2. A turbo pump has a mechanical blade that is rotating at a very high speed and pulls the gases out of the system, imagine a jet engine on an airplane. The cryo pump is efficient if for ultra high vacuum ranges >10^-8 Torr compared to turbo. Both pumps require a small mechanical pump attached to the chamber to provide the lower level vacuum in the 10^-3 Torr range before they take over.