Changes that you make while in your website’s editing mode are saved automatically. This means you don’t have to go through an additional step to save the changes you make.
If you want those changes to appear for visitors on your ‘live’ website, please click the button Publish in the top right corner. This has the advantage that you may continue working on your Jimdo website “unseen” as long as you don’t click that button.
If you actually change something by accident, you can always undo the previous steps.