It can be helpful to see the outline of your objects on the page as some objects may be layered below others. There are two things you can do to see all the objects on the page.
X-ray mode applies a temporary grey overlay onto the editing page. This makes it easier to see all the objects in white to help identify them more easily. Use shortcut CMD+OPT+X (on Mac) or CTRL+ALT+X (on Windows) to activate and deactivate x-ray mode.
Once you have X-ray mode on, you'll be able to see all the objects on the page. This will allow you see and re-arrange the objects if an object is at the bottom of the page or hiding on the sides. Click once on your page then use CMD+A (on Mac) or CTRL+A (on Windows) to select all objects on the page.