Hex saves every change you make automatically, so there is no need to obsessively "Save" just to preserve your work.
By default, projects have a simple but powerful version control engine built-in that lets you see what's been changing in projects and restore to earlier versions.
Version and edit history can be found in the left sidebar of Hex projects, in the History & versions section. Versions, edits, and comments are all presented in a chronological timeline, with brief descriptions of who made changes and what they did.
To access previous versions, select that version from the timeline. This will open the version history dialog where you can view historical versions.
When viewing a historical version, you'll have the option to restore the project to that version.
While Hex automatically saves every change you make into "Autosave" versions, you can also optionally create named versions by choosing Save version from the History & versions sidebar tab.
Publishing a version of a Hex project is similar to saving a version, except it also updates the currently-live version of the app that users will see. Read the Publishing page for more details. Every publish creates a new version.