MIDI is a port you can find in the back that looks like this. Some keyboards come enabled with a standard usb printer cable, but you can find converters pretty easily.

you need a midi connection? http://www.amazon.com/Cable-Converter-Music-Keyboard-Window/dp/B0017H4EBG

load up drivers boom bang you can use the keyboard as a device on your pc, but you need a daw or some program to use it in!