How to Assign an User
First, you need to create the user from your Control Panel first
1.) Loggin into your Control Panel
2.) Click on "Hosted Organization" menu
3.) Select your Organization name / Domain name
4.) At the left pane, click on "Users"
5.) Create the new userWhen the user has been created, go to your Sharepoint site ,~ Loggin as administrator~ At the top-left corner, click on Site Actions >> Site Permission~ Select the Grant Permission menu