After a page (or master, etc.) has been checked out and edited, you can save those changes locally using File->Save. This saves the changes only to the local copy of the shared project on your computer.
When you are ready to submit your changes to the shared project directory, you can check in the page. To check in a page, right click on the page in the Sitemap pane and select Check In. After the page is checked in, others can update their local copy to view your changes. You will also no longer have the page reserved for editing, and others can check out the page to make their changes.
Checking in a page may require you to check in project properties that you have checked out as well as new pages or masters that the page uses.
To check in multiple pages, select the pages in the Sitemap, right click and select Check In.
To check in the entire project, go to Share->Check In Everything. This will check in all of the pages, masters, and project properties that you currently have checked out.