Positions an entity at an absolute position in 3D space.
Entities are positioned using an x,y,z coordinate system. x, y and z each have their own axis, and each axis has its own set of values. By specifying a value for each axis, you can position an entity anywhere in 3D space. 0,0,0 is the centre of 3D space, and if the camera is pointing in the default positive z direction, then positioning an entity with a z value of above 0 will make it appear in front of the camera, whereas a negative z value would see it disappear behind the camera. Changing the x value would see it moving sideways, and changing the y value would see it moving up/down.
Of course, the direction in which entities appear to move is relative to the position and orientation of the camera.