To add more pages to your design in InDesign, open the Pages panelvia Window>Pages. You can add more pages using the plus icon at the bottom of the control panel. You can delete the pages you have selected using the icon with the garbage can. You can also change the order of the pages by clicking and dragging selected pages.

You can also select the Insert pages ... option via the context menu (horizontal lines) in the top right-hand corner of your control panel. In the dialog that now opens, you can also make selections for quantity, positioning and sample pages.

Important: If you want to add more pages to your design, make sure that you expand the document pages, not the master pages.