To bookmark a layout that you wish to use on a different time, select the Layout option on the left-side panel in the designer. Once selected, you can either search using a keyword or browse through the list of layouts you think will work for your yearbook:

Click on the magnifying glass icon to see more details. In the pop-up window, toggle the “Bookmark Template” option to check it:

After that, you can close the window. To make sure it’s saved, scroll up and go to Bookmarks, and you should be able to see it there:
 

This is the same process as Bookmarking a Template, Elements and Background.