Go to the user you want to assign the roles to and then click the Roles button, this will navigate to the Roles page.
Here you can add the roles to a user. The roles you have to add depend on the type of user you're creating. Search and select the roles from the left and click Add selected to add roles to the user.
You can check this page to see the roles you need to add to a user: https://ccvconnect.freshdesk.com/a/solutions/articles/43000582522.