Entities allow you to control the organisations that can log in to your channel. Every Individual User that you want to give access to your channel must belong to an Entity (ie you need to set up an entity first, in order to then setup an individual's access).
To add a new Entity, go to Organisation/Entities:
Click the 'Add' button to create a new record:
You will be presented with a new empty record to complete the details of your new Entity. The mandatory fields are denoted by the * on the field name. Remember to click SAVE when you have completed all the details.
Note that once the entity is created, you can add Users to this entity (scroll towards the bottom of the record). For more information about creating User profiles, click here.