Welcome to Android Central! Which phone? Are you using the launcher (i.e., the homescreen interface) that the phone came with, or did you install an alternate launcher like Nova Launcher?
Usually, you can add an additional page by dragging any icon over to the far right of your rightmost homescreen. That should create a new homescreen. On other launchers, you can manage your homescreens by pinching first, which shows you an overview of all of your homescreens. You can usually tap a blank homescreen with a "+" in the middle of it to add a new homescreen.