The physics plugin is responsible for calculating real time physics simulation with the help of a 3rd party library called Bullet Physics. Bullet Physics is an open source physics library by Erwin Coumans, with support of collision detection, rigid body and soft body dynamics. If you are excited, you can find more information about the library at https://pybullet.org/wordpress/, and download the source code from https://github.com/bulletphysics/bullet3.
For now we are only concerned about rigid body dynamics, and obviously for this, we need collision detection as well. With the plugin you can easily add a rigid body for your geametry (practically you add the geometry to the rigid body object). You can even use complex mesh geometries on your scene, and load them through the Assimp plugin, as you will see in the following sections. The plugin also implements a low level supporting for liquid simulation, wich is not more than a simple bouyancy force generator. Lastly, if you're interested in the source code, you can find it at the \ApertusVR\plugins\bulletPhysics folder.