2 Answers

What are Karma points?

As you contribute to the community your profile accumulates Karma points. These points distinguish you as a respected member and one which opinion is highly regarded by the community. Gaining Karma points also opens up doors to some cool features in akaQA which are constantly added.
Here's how karma points work:

Each "Thumbs Up" on your question or answer yields 15 point.
Each "Thumbs Down" on your question or answer yields -35 point.
Each "Thumbs Down" on someone else's question yields -10 points against your karma points while removing 35 points from them.

Number of daily votes

The number of daily votes you can give is limited and grows as you gain more Karma points.

Note about the thumbs down 

Thumbs Down are reserved for vulgar or inappropriate questions or comments such as racist remarks or remarks that are hurtful to any member or user of this site. They are not to be used just because you do not agree with someone's opinion. Opinions are allowed here under the member voted freedom of speech within reasonable boundaries rule.

It is how we keep tract of who gives good honest answers, if you get a good answer give a thumb up and that gives the person karma points if you give a thumbs down it will take them away but you will lose some also so use wisely. OK to give a funny answer a TU too. Don't forget to click thumbs up ONCE to thank those nice people. Clicking twice doesn't double it, it takes it back.

Only use thumbs down for bad language or abusive remarks. Not just because you disagree with a remark.