Hi Carol,
Changes made in Studio are auto-saved and happen continuously. When working on the same branch as the branch where studio is enabled for in Studio Pro the changes can be synced when you click update or commit. The revisions are not viewable like the Pro revisions because you do not provide it with a comment. Also note that Studio is no longer supported since version 9.20.
https://docs.mendix.com/refguide/collaborative-development/