In a multi-entity plan, a user can be created in more than one entity, and can have different permissions in each. 

In order to work in each entity, they need only log in as normal , then switch to the correct Entity via the  icon in the Ribbon , or via the menu option; Basic settings > Entity > Change entity . 

To switch entity, just double click on the desired entity or select it and then click the icon. 

To effect the entity transfer, the user must have a user record in the table USR with this entity.

Only such entities are selectable.

See below for a walk-through: