For day trading, you ideally need to understand 3 ares well:

1. Fundamental analysis
2. Technical analysis
3. Trading psychology

Every financial asset that you are trading will have specific patterns which you can learn and either skills will give you an advantage.
How do you obtain such knowledge? Start reading sites such as http://investopedia.com

Then you will need to choose a platform for trading the assets you wish to trade e..g. MT4 or regular currencies.

These platforms usually allow you to create a guest account and will give you some virtual money to test your investment skills and platform. e..g virtual demo money for USD$ 5000. Learn the platform and test with the virtual money and trade it with discipline as if you are using real money. If you start bad habits, they can be difficult to lose.