After enabling this integration, you can attach files to cards from your DropBox in the same way as you would any other file.
Clicking DropBox from the files drop-down menu will open your DropBox account in a new tab.
Browse the file you wish to attach to your card, and press Choose in the bottom right corner (you can choose to attach multiple files at once if needed).
After pressing Choose you will be taken back to your card inside Favro. By pressing the menu button on your attachment you can choose to download, delete or open the attachment in DropBox.