Hello Mikail,
Regarding merits/demerits... What are they? Well, from The American Heritage® Dictionary of the English Language, 5th Edition
noun
Superior quality or worth; excellence.
"a proposal of some merit; an ill-advised plan without merit."
A quality deserving praise or approval; virtue.
"a store having the merit of being open late."
Demonstrated ability or achievement.
"promotions based on merit alone."
Merits are a way for your fellow members to indicate that a post that you've made was superior. It's a way of showing their approval. Conversely, demerits are a way of showing disapproval.
If you see a post from a person with a lot of merits you might reasonably assume that individual is well thought of here at ravishu.
As far as what they're good for... well, nothing really, it's just a reflection of how they're thought of.
I hope that helps.
--
Eljorn