Overheating engine. 2005 Pontiac Bonneville what would cause my engine to overheat?

You should first try to locate where the coolant on the ground is coming from. It may be a leaky hose joint that can be tightened or many other things - blockages, leaky heater core or radiator, stuck thermostat, bad water pump, air in the system (if work has been done just previously), bad radiator cap, bad temp sensor, defective cooling fans........take you pick. But first try to determine where the leak is coming from and, if you are seeing a trouble light, have the car scanned for any codes.