The Save Page function saves the changes to the webpage on which you are working. Unless and until you have saved your page you will not be able to preview or publish the page.

Note: If you have made changes to the document, and you have not hit the save button, and then you navigate away from the editor to another page, you will be prompted to save your changes.  By selecting OK your changes will be saved. This automatic save, which appears under certain circumstances, such as described above, may fail to save your pending changes under some circumstances and should not be relied on as a method for saving.