You can copy a card, and paste it to the same or another folder.
Folders and groups cannot be copied.
Long press on the card you wish to copy in order to select it and access the menu.
Choose "Copy" from the menu.
Navigate the folder structure as normal and press the red "Paste" button to drop the item into the currently displayed folder.
The pasted card will be placed in the first visible group at the top of the screen.