To add an image to your template click on the IMAGE button in the top toolbar. A Gallery popup will display showing any previously uploaded images for your account. You have the option to upload new images, choose from existing images, and also to use images from your Facebook and Instagram accounts. Select an image to add to the template and click on the "INSERT" button at the bottom of the popup. The image will then be added to the middle of the template.
The image object can be moved, resized, rotated, edited and deleted. Right-clicking on the image exposes a full menu of options allowing you to edit, delete, clone, and change the layer order of the image.