For every company allowed to access EPIC portal, the first user will be created by Elia.
This user is a Super User (SU) for it's own company benefiting from all permission and access rights for his company.
Once this SU has been created for he is able and accountable to invite new users from his company on EPIC.
When creating new account for another company member, the SU has to decide which rights he wants to give to the new user (Super User (SU) or Basic User (BU), for the difference refer to question What is the policy in terms of user rights?).
For the creation of a BU, the SU creating the new account has also to manage the access and permission rights (e.g. determine the applications within EPIC to which this freshly created BU has access to). He can do it directly or at posteriori. Any SU can modify the access and permission rights of any other BU at any moment (cfr. How can I manage permissions of other users within my company?).
To invite a user, follow these steps:
#1 : Go to the “Accounts” tabs 
#2 : Choose the company to which you want to add a new user, on the upper part of the screen showing the company to which you have access
#3 : Select the button “Invite user to your organization”
#4 : Fill in the information about the new user and grant him the needed access
#5 : Finally, accept the terms and conditions