Click Save button in the top right-hand corner of the subtitling editor:
This will save a new version for the video and language you have been working on. When the subtitles get saved, you will see the pop-up displayed below:
After this, you can either close the editor and resume your work later (by clicking Exit button), or continue your subtitle session from the place where you had stopped before saving (Resume editing).
Important: After you click Save button, your subtitles will always be marked as incomplete - the language will be labeled with a yellow or red circle in the list of languages. To mark it as complete, please use Complete button instead; it will both save a new version and mark the language as complete.