I have water coming from my AC unit, and it is leaking onto my basement floor. Why is this? How can I fix/stop this?

Thank you.

Check to make sure the evap coil drain is not plugged. If it is plugged water will overflow from coil drain pan and run down inside the furnace.

Where is that evap coil drain?

Your evaporator coil usually sits directly on top of the furnace. There should be a drain line or hose coming out of the sheet metal on top of your furnace. Usually directly below the two copper lines that go into sheet metal on top of furnace.