The administrator of your Clickatell account will have the ability to invite users to the account by clicking the profile icon in the top right of the portal and selecting User Management.  From here you can add a new user and assign roles to the user.

Clicking the 'Invite User' button will send an email invitation to the user. The email contains a link directing the user to the sign-up page where they can set their password and gain access to the portal. What users can access on the portal is determined by the roles you've assigned to them and the permissions and level of access associated with it.

You can edit a user by selecting the user from the user management table.

If you are currently using the old user portal:

The administrator of your Clickatell account will have the ability to invite users to the account in User Management. Once users have been added, they will receive an invitation email with a setup password. They can now log into the account with their login credentials and use features based on the privileges assigned to them.