First you have to receive merits, and then you can give merits. For every 2 merits received, you can give 1 merit.
To give merits to a post, simply click on the "+Merit" button, which is located next to the "quote" button.


Now the most important thing, before you start giving merit, is to make quality posts to be able to receive merit. To do this, try to get involved in the themes of the topics, share information you have, and raise questions that you find useful for yourself and others.