Revisions are managed in the Project Explorer interface via the Revisions tab at the bottom of the interface:
Revisions are a way for you to track changes in a SIX Project. A Revision is a copy of the Project file at "that state in time". The primary reason for creating Revisions is to be able to compare two Revisions of a Project and create a Change Order report.
Every Project starts at Revision 0.
Revisions are intended to be used after you have "sold" the Project and you want to then track changes between the "as sold" and the "as built" Project.