What is Karma and how do I earn more?
You earn karma by doing things that help the site community like answering the free polls. Soon there will be other ways to earn karma like having people vote up comments you make about a question, closing out a question promptly, and getting a question published.
How are worth and the leader board calculated?
The leader board is refreshed multiple times per day and uses your total worth: the sum of your "current holdings" + "total cash." Your current holdings is what your positions are currently worth if you were to get out of them at this moment. Your total cash is money you've made from previous transactions (or that was granted to you) that is not currently being used.