Open the reservation you wish to send the confirmation from then click the config cog beside the reservation # then select Send Confirmation to continue.
The Email Confirmation window will now display with your pre populated email from a document you created under the documents page under setup.
You can modify this specifically per reservation if you wish by simply clicking in the text field and adding/removing any information you would like for them to see. Once everything that is needed is in the email click the Send button and the confirmation email will be sent to the customers email address listed in their contact information.
Note: Online reservations are automatically sent a confirmation. In-house reservations are automatically sent as well if the email address is filled in. However, in-house is on a 10min delay to allow for time to make a payment, then it's sent automatically.