What are points used for?

If by reward, you mean some sort of compensation or prizes, then you'll be disappointed. Points are good towards nothing tangible. Not cash, Apple products, coupons towards products, or anything worth even a dime.

They really have only one value. When you reach Level 6, you have access to the The Lounge. There, discussions can be more relaxed about various subjects (not just technical stuff), and access to the hosts.

I’ve honestly found access to the Lounge to be rather overrated. The most useful thing earned from points is the ability to report posts - basically help the hosts edit out things that should not be posted like spam or people sharing info they shouldn’t be sharing.

Beyond that.....oh the points get you more dots beside your name that well, just are more dots by your name. And you can eventually have a custom avatar if you wish.

You can do nothing with points.

See: https://discussions.apple.com/learn

Just adding a short answer:

Points are pointless (my personal opinion).......