Before people on your team can sign in and use your organization's Google services, they need a user account. There are several methods to provision users to Google Workspace:

1. The easiest way to add user accounts is to add them individually in the Google Admin Console. Read this Google Workspace support page for more on this.
2. If you have many users, you can add their accounts all at once from a spreadsheet or CSV-file. Read this page for an overview.
3. On that page you will also find a way to use LDAP synchronisation.
4. If you are keen on using API's, try Google Workspace Provisioning API which you can find here.