The answer has been posted somewhere before Now https://bitcointalk.org/index.php?topic=2818350.0

You get merit points when someone sends you some for one of your posts. Additionally, when someone sends you merit points, half of those points can be sent by you to other people.

Certain users are designated as "merit sources". They can create new merit out of nothing, up to a limited number per month (which differs per source). I will not be posting a definitive list of merit so