How do you earn forum points?
It seems like just being idle for a while makes them go up?

Well, there's an explanation of the account system: https://n.ht/t/5
Forum points will grow based on two methods, because there are quite a few lurkers from the old forum:

Active Members: Those who like to communicate, participate, and enthusiastically help others by answering questions in the community. These users can quickly accumulate contribution points, level up to higher ranks, enjoy more privileges, and continue to have an influence in the community.
Lurkers: Those who prefer to quietly read posts and rarely speak up, but still diligently absorb the community's content and silently contribute to its growth. In traditional communities, this type of user doesn't compete or seek attention, is most easily overlooked, and feels the least sense of belonging. For these users, we've added a reading growth system and an automatic check-in growth system. NHT recognizes the contributions of lurkers in a gentler way.