Ticket ratings have been available since quite a time and that is how it works.
To automatically send tickets out after closing a support case, the ticket needs to be closed for good. Means a soft close won't send a rating email to the client.
It is also important that whatever language you have set in your operator panel the language phrases need to be available for the ticket rating email template.
There are two ways to send a rating email:
The cron job file will send a rating email when the reopen possilbilty is over, depend what your settings are in your operator panel - settings - support settings. It can take up to 30 days for the email to be sent.
When closing a ticket in the operator panel, make sure you use the closed option.
When you receive a rating from a client it will show on the ticket itself and change your overal rating statistics on the top right of the ticket view.