Preview Function is used to preview a page/post. Once you have saved your draft, use this function to see how your page/post will look.

Click on Preview. It will display different views of  the Preview function.

Desktop: By default, the Desktop view will be selected. When  selected, you will see how the page/post will look on the desktop as following:

Tablet: When selected, you will see how the page/post will look in the tablet as following:

Mobile: When selected, you will see how page/post will look in the mobile as following:

Preview in new tab: When Clicked, you will see the page/post will be opened in the new tab as following: