You create an invisible entiy called "pivot" as a parent then you attach children entities to it
For example in a solar sustem the pivot can be the sun origin while the earth is a child
You rotate the pivot and the earth turns around the sun
This is a simple example but beleive me it is a powerful tool
In an other thread I have been suggested to move in MED the center of the model
It can work for a door, for example, but it is not a general purpose solution