Here's a step-by-step guide on how to add a new user in your Microsoft 365 tenancy:
Go to https://admin.microsoft.com/ and sign in with your administrator credentials.
Click on "Users" on the left-hand side menu and select "Active users" from the dropdown.
The "Add a user" button can be found on the top right corner of the "Active users" page.
Enter the user's first and last name, display name, username, and password. You can also assign licenses to the user at this point.
Select the appropriate role for the user. The default role is "User", but you can choose from other roles such as "Global admin", "Billing admin", "Password admin", etc.
Select the user's location and language from the dropdown menus.
Check the box that says "Send password in email to the new user" if you want to send a welcome email to the user with their login credentials.
Once you have filled in all the necessary details, click on the "Add" button to create the new user account.
Congratulations! You have successfully added a new user to your Microsoft 365 tenancy.