There are three ways to upload an image.

Option 1:

Step 1:

Click on '+Add Photos' icon.

Step 2: 

upload photos from either the Local Disk (your computer), Facebook, Instagram or Flickr.

Option 2: 

Double click on the photo icon. You will then be able to upload photos directly from your computer. You are able to upload multiple photos at once. The box you have selected to upload photos from will be filled with one of your selected photos while the top remaining will appear on the top panel. 

Option 3:

You can simply drag and drop photos from you computer to your selected page.