The snapshot is a backup of the planning captured at the precise time. You can proceed with the planning after you've created this copy. During the planning process you have always the possibility to return to the original state of it using the stored snapshot. The creation of a snapshot is reasonable if you make a lot of changes to the planning. So if something goes wrong with the planning, you can restore it with a snapshot which was working previously.
This is how you can create a snapshot:
Open an existing project or create a new one.
For more information on how to create a project see Create a project.
In the project, on the Start tab, in the Section group, click Planning.
For more information on how to create a planning see Create planning elements.
Now you can see the stored picture on the snapshot-axis. Click the name of it to open:
Click Revert to reconstruct the original planning.
In this case all changes made to the planning will be deleted.