The list on the right hand side contains all Resources with access to this instance or instances, hence it is clear which resources do not currently have any work assigned.  Drag any Resource over an item in the planner to re-assign it.  However over a Resource to display their email address, click on it to generate an email.  Click on a Resource to display a panel at the bottom of the display showing their workload, this is useful when viewing the entity planner, see below.  Limit this list of Resources using the Roles drop down on the toolbar.