Points

How do I earn it to use different communities?

My way is just commenting a lot. All my favorite subs have no threshold for the minimum karma.

person say useful or funny thing? updoot number go up

A useless Internet point.

its good if you have a good amount so you're eligible to participate in sub's. after that it's meaningless.

the way I got karma was by posting my real tragic events in my life or commenting a lot. honestly didn't expect them to blow up and I don't really care.. i just vent or comment my thoughts. usually i get downvoted too but like I said it's meaningless after you're able to join certain subreddits.

What it is about i must be killing it somehow.

Near as I can tell, people can use them to pay rent, afford luxuries, and generally feel better about themselves.

I haven't found what places accept reddid karma as currency, but I'm sure they exist as hard as some people get upset when they don't get as much.