To add your collaborators you have several solutions that I will present in this documentation.
Create users manually
You have the possibility to create users manually one by one.
This way is rather used if :
You create other administrators of the platform
You want to test the solution on a few users.
You don't have many users to create.
Import users using a CSV file
This solution allows you to import large numbers of users by listing them on a GSheets or Excel.
Synchronise users with Google Workspace Groups
This solution allows you to synchronise your user groups already present on Google Workspace.
If you add or remove a user on Google Admin the synchronisation will be automatic.
Synchronise users with Microsoft Azure AD Groups
This solution allows you to synchronise your user groups already present on Azure AD.
If you add or remove a user on AzureAD the synchronisation will be automatic.