You can get merits on any post because merits are sent from users, if they like what are you posting then you will get merits.

Some users like to only post in giveaways and bounties, that kind of post doesn't give merits at all... so, the best way to get them is by sharing high-quality info. And merits are required to grow your account, if you want to be legendary someday then you need to get 1000 merits.