Once you have selected a Source Folder and loaded images into your Gallery it's now time to start adding images to your post, you can do this in one of two ways:
Method 1: Double-click
Double click on an image in the Gallery, your image will appear at the bottom of the stack in its own row.
Method 2: Drag-and-Drop
You can drag-and-drop and image to wherever you would like to place it, if there is already an image in the post, blue lines will show up to indicate where the image will be placed.