Here's how it works:
The lightbulb stands for "insightful" or thought-provoking.
The happy face is for something "funny" or cool.
We will be adjusting the user karma/points totals to be give you 2 points for receiving an "insightful" vote and 1 point for a "funny" vote. Then if something is bad, use the report button to report it.
We're also in the midst of tweaking the algorithms for the front page so it interprets both votes correctly, but this part is technically difficult because it's one of the most basic functions of the site, so it has to be pushed through about 5 layers of programming languages before it'll work, and figuring that out is a bit tricky.
However things look to be on track. The votes are working right now, please start using them and feel free to give feedback right here.