This is a small board designed to boost 3-8v (typically 5v) up to 12v. In addition, it contains a N-channel mosfet which can be used to turn a device on or off or to perform PWM on something like a fan.
This board was designed to efficiently power 12v computer fans using as small a footprint as possible. While it's certainly possible to go smaller, this uses 0603 and larger devices.
On the input side there is +5, ground and a FET control line. To enable the FET as a ground type device, pull the FET control line to 3v or higher and connect the device between +12 and FET-. Note that when the fet is not activated that the FET- will not provide ground.