The image manager allows you to bulk upload images that you wish to use in your emails.
You can upload these images to the Root folder or to a subfolder (shown above). Either select the existing subfolder to upload to, or click New Folder to create a new folder to add images to.
Once your images are in the manager, you can move them to subfolders if needed or delete them. Moving an image will not affect the image's URL, so you don't have to worry about the image breaking—it will still be accessible. Deleting an image though will remove it from the Image Manager and it will not display where currently used.