Once you have added the Image Relay App to your Box account, you can send files or folders to Image Relay from within Box.
Hover over the the files or folders you want to share.
Click More > More Actions > Send File / Folder to Image Relay.
You will then be prompted to Sign In to your Image Relay account.
Select the Image Relay folder you want the files to reside within or create a new one. You can add metadata at this time too.