There are a variety of options for saving content available from Save menu in the content editing window.
If a change has been made to the content and it has not been saved, then the "Save" button will be highlighted, as shown in the image below. Just click Save to save the changes. If a visualization is shown for this content, as it is in this example, then the visualization will be updated to reflect the updated content.
A number of the other Save options will be available in the Save menu even if the menu itself is not enabled. For example, you can save another copy of this content or rename it.
Here's a list of the available Save options.
Save snapshot to edition
Save and create another
Save and close the content. Create a completely empty form for this content type. In the case of content, for example a carousel, that is the "parent" to "child" content such as the individual carousel slides, "Save and create another" is only available for the child content.
This item is only enabled if the content has not changed since last saved.
Save and close
Save the current content, close the window and return to the content library. This item is only enabled if the content has not changed since last saved.
Create a new version of this content, including the same values for the fields (in this case headline and strapline) and the same assets
Choose a new name for the content and save it.