There are 3 options for saving and closing a web page:
Save: Save changes to the page and exit edit mode
Save and Keep Editing: Save changes to the page and continue editing
Stop Editing: Exit edit mode on this page. You will be prompted to save or discard your changes.
When you open a web page in edit mode, it is checked out to you. The status bar shows that the page is "checked out to you" and "only you can see your recent changes".
When a page is checked out to you, other permitted users cannot see your changes, and cannot edit that page until you check it in.
Check In options:
Check In: Check in the page which is currently checked out to you.
Discard Check Out: Discard any changes you have made to your checked out version.
While you are working on the update and save your page, your changes are not visible to the public. You need to publish your page for the update to be viewable by the public.
Select Publish tab and click Publish.
SharePoint creates a minor version of a page each time you check it in. And, a major version is created each time you publish a page. The current live page is the latest major version.
Major versions are always in whole numbers, such as 1.0, 2.0, and so on. Minor versions are denoted by decimals following a major version number, such as 1.1, 1.2, 1.3 and so on. Supposed the latest minor version is 4.3, when you publish the page the next major version will be 5.0.