While you are working on subtitling or translating a video in a certain language, you most likely click Save button in the editor a few times. When you do it, Amara saves a new version of your subtitles to the server without overwriting the previous version, which also remains stored on the server.
A subtitle version includes the video title and description in the language of the subtitles, subtitle text, and subtitle timing. A version can have no timing, or even no text at all - you can remove all the subtitles in the language and save. In the latter case, the language without subtitles will disappear from the list of languages available for the video, but the link to the language page will remain in the activity log for the video:
You can browse past subtitle versions, compare them with each other, download any version of your choice, or return to any previous subtitle version at any time. This is why you need not be afraid to make a mistake while editing or uploading subtitles - you can always overwrite subtitles that have gone wrong with another version, or return to an older version!
The changes you make between clicks on Save button exist only in the memory and browser storage of your computer. They will not be stored on the server until you click Save, creating a new version.
Every time you upload subtitles from a file, you also create a new subtitle version.