Locate the user you would like to add permissions to and click on the shield icon to the left of their username.
You will then be taken to a screen that displays the permissions that user currently has. To add one, click on the dropdown arrow below 'Security Roles'. Locate the permissions you would like to add and click on it.
Then click the blue button that says 'Add Role to User'. The page will refresh and you will notice the new permission will be listed under their permissions.
Then click close.