Adding a user in Microsoft 365 is a simple and straightforward process.
Before you begin: Be sure you have an available license for the product you want the user to have. You can check this by going to licensing.
Go to the admin panel at admin.microsoft.com and sign in as a User Admin or Global Admin.
Go to Users on the left hand side.
Click "Add User"
Enter the user's details and click "Next"
Choose the license and, if necessary, and administrative roles the user needs.