I've discovered Bitcoin few days ago, but I am skeptical about few things, why would I invest money in Bitcoins at the end of the day,why would I convert money into Bitcoins?

If I want to buy stocks or invest money I can easily invest with real $. Why would I convert my $ to bitcoins?
If I want to gamble , I can simply gamble on websites that require $ as currency, why would I convert it to bitcoins?
What's the difference between Bitcoins and dolars? What does bitcoin bring to the table that real $ don't, less taxes, more income?