Rapberry Pi is a versatile low cost single board computer that plugs into your TV and a keyboard. It can be used for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video. Besides that it has many GPIOs to to receive signals and outputs to control or activate other devices or peripherals.
Most GPS/GSM vehicle tracking units are available in 12V system. For truck and trailers which uses 24V battery, the voltage need to be stepped down to 12V.
In addition to this, the GPS tracking units need to have back-up power when the main battery is cut-off during theft.