What is the unit of accelerometer module output
Accelerometers measure acceleration. Integrate twice for position with respect to time. Doing that for each axis provides a 3D position.

In theory. For the real world it's not even close to that simple. Doing a simple double integration will be reliable for less than a few seconds. If you want to find out a better way, then you'll need to ask a different question. Though you'll likely find it answered on this site already.

Typically accelerometers are not used for this because it's so unreliable. What people usually use are cameras and motion capture.