Alternatively you can click on the 'Page' menu and select 'Insert' (or press Ctrl-I on your keyboard). This will add an extra two pages before the page spread you are on.
You can also remove pages via the "Page" menu in the top menu bar (or by selecting the spread and pressin Ctrl-D on your keyboard).
For clarity, a page is considered one side of a sheet of paper and are always added in pairs and cannot be added individually.