To begin, log into your Office 365 site using an Admin account.

From there, open the root site of SharePoint Online and expand the Admin dropdown menu on the top menu.  Select the Office 365 menu.

Next, go to the Office 365 admin center.

Expand the Users section on the Dashboard and select the Active Users menu.

Click on the New (+) icon.

Enter the appropriate information onto the User Account form. When finished, click the Create button.

After you click Create, you will get a message that the new user was successfully created. The message will include the new user’s information.

Please note that by default, Office 365 will automatically create a password for you.  You are able to edit the password after you click on the Close button. In addition, user information can be edited by clicking the Edit button.