I have manual payment set up. When user completes his order inside the cart he gets an email with details of his order and how to make the payment.

But what about the next step when I get the payment and I confirm his sale order? The users don't get any email. How to achieve this? Do I need write custom module/automatic action for that or there is actual workflow to set up? The confirmation mail template seems to be written in such a way to handle both confirmed and not confirmed orders but is send only once.

It would be weird if Odoo didn't had such basic functionallity as notifying about each step in the order life cycle.