To learn how to trade penny stocks properly, you need to familiarize yourself with the Pink OTC Market (frequently referred to as the Pink Sheets) and the OTCBB (Over-the-Counter Bulletin Board). Then you need to find yourself a broker.
In may seem contradictory, but when you first get started you want to pay more for your penny stock broker. Go with a full service broker like Fidelity or Charles Schwab so you are provided more research tools and more robust support in the learning process. Yes, this makes it more expensive at first, but in the long run you’ll appreciate the knowledge and wisdom gained.
Then you need to practice trading with paper trading. There are many applications for paper trading (trading without money), or your broker may provide you such a system. Be sure to research and practice before you put your real money on the line.