Align
An Alignment command will allow you to force the face of one object to be in line with the face of another object. (Typically works with flat faces)
Mate
The mate command joins the face of two objects together. These faces will be fused and unable to separate.
Centre Axis
The Centre Axis command will allow cylindrical geometry to be centred with other cylindrical shapes.
Offset
The offset tool will allow you to set a distance between the face or edge of two objects. The two 3D Models will not move closer or further apart from the distance set.