When you open an account, you are the account's owner. In the Heureka portal, click on 'Profile' and you should see a 'Team Members' tab. Here, you can invite new team members to join your account via email. Once they join, they will have access to your account credits, but, their data will remain private to their profile and won't be shared across users in the account (unless they upload files to a shared workspace or add collaborators to a project). Adding users is free and there is no limit to the number of members that can join your account.