Fill it up with coolant (50/50 anti-freeze/water). Enjoy!
The water pump on my car developed a leak in its rotating seal and started to hemorrhage coolant. Here's how I replaced the water pump.
Step 1: Disconnect the battery
Disconnecting the battery is a good first step for almost any car repair. Now you don't have to worry about shorting/frying anything expensive or pesky radiator fans turning on and chopping your hands off.