To quickly add all photos from a folder:

1. Click Projects on the main menu at the top of the page.
   
   
2. Select the project you would like to add photos to.
   
   
3. Click the Edit button near the right side of the page:
   
   
   
4. Navigate to Photos:
   
   
   
5. Click on Add Photos near the right side of the page:
   
   
   
6. Navigate to the folder that contains the images you want to add to the project. Toward the bottom of the dialog, click the phrase Fill Project:
   
   
   
7. Click the Add Selected button to add the images to the project:
   
   
   

You can change the order of photos in the project by dragging and dropping.