There are three roles of users in Kanban for WordPress – Users, Clients and everyone.
Users have write access to any board they’re assigned to. They can make changes to anything editable on the board.
Clients (Requires the Advanced User Management add-on)
Clients are users who only have read access to the boards. This means they can view a board, but cannot make changes.
Everyone (Requires the Advanced User Management add-on)
If a board is set to be public, then anyone with the URL to the board can view it. However only users who have accounts and are granted write access can make changes.