Can you give me an example?
Say you've posted a link in the Design channel. When your friends click on it and give you feedback, you'll get points in Design for it.
How much is a point?
Each action has a different point value. For example, re-sharing a link gives the highest number of points (compared to clicks, pluses and replies) because it's a really good indicator that a link is worth spreading.
Why points?
Mento uses all of this information to find the most interesting links and people in each channel. That's in part how Mento determines what links are popular and how Mento makes recommendations to you when discovering new things.