Placker works with cards that contain information in the form of attributes. There are most commonly used attributes (such as due date, member, etc.) and less common attributes.
When you single-click a card, a panel will be opened on your right. There, you can click Show empty attributes to be able to edit and view all the attributes.
Another option is to double-click, so you will find the card in a pop-up view, which also contains the card attributes.