Star:

When you read a post, at the bottom of the top box, you'll see "Vote:"

1 is low, 5 is high. Based on one's judgement of the level of contribution to the hub, click the appropriate star. This effects points & rank.

Recommend:

At bottom right reading a post, if you feel it's an informative post, whatever; click recommend left of report vio. This also helps points/score/rank.

It's a merit system with a formula used by admin to rate members.

Happy posting!