When you are done editing an object you should unlock it the object to make it 'current'. When you do, the original object gets unlocked and 'replaced' by your working copy. From that point on, others can view and edit the new version of the object. This basically concludes an edit cycle.
At this moment you may wonder what happened to the old version. To be precise, it will not get destroyed - hence the quoted replaced - but stored in the ITP/MDK Repository as an older revision. This means that you do not have to worry about losing important versions of your objects.