The Page Editor includes a ‘Save as template‘ button which can be used to create a custom Page Template. This appears in the upper left hand corner of the editor, and is represented by a export symbol.
Before saving the template you should configure your page to contain the items you wish the template to contain. Note that any settings specified within the items (e.g. Name, CSS class) will also be retained, allowing you to configure the items as little or as much as you would like.
When the page is ready to be saved, select the ‘Save as template’ button. This will prompt you to enter a name for the template, or choose an existing template which you would like to overwrite.