Reply to Which capacitor for LED's?

Hello all! I am getting started on a DIY midi controller soon and have everything I need together. The only thing I am unsure about is the capacitor. I hear that I should go with 330ohm but I do not know much in this area. If it helps, I am planning on using around 20 LEDs for my project. Power source would be the USB's 5v supply.Any info would be greatly appreciated!