Manuscript versions are restore points for a section of your book. Save one before a big revision, and you can always roll back to it. This is separate from worldbuilding versions, which track how your world changes over the story.
What versions are (and aren't)
A version is a saved copy of one section's text that you create yourself. Versions are not saved automatically while you type, apart from one exception: whenever you restore a version, Writing Crucible first saves a backup of what you had, so you can undo the restore.
Saving a version
Open the section in the Manuscript Editor.
Click Create Version in the toolbar.
Enter a Version name (required), and optionally some Comments about what's changed.
Click Save Version.
Each version stores the section's text, its word count, the name, your comments and when it was saved.
Restoring a version
Click Restore Version in the toolbar.
Pick a version. Use the search box to filter by name or comments.
Click Restore Selected.
Your current text is backed up as a new version before the restore happens.
If you see No versions yet. Create one from the toolbar., this section has no saved versions. No versions match your search. means your search filtered them all out.
Version history by plan
Free: not included. You'll be offered an upgrade when you try to save or restore a version.
Plotter: versions are kept for 30 days.
Author: 90 days.
Professional: kept indefinitely.
On the Free plan, if restoring a version would take your manuscript over its word limit, the restore is stopped and you'll see a word-limit warning. The backup of your current text has already been saved at that point, so you lose nothing. This applies to every section, front and back matter included, whether or not Counts is ticked.