"Burping" the cooling system allows trapped pockets of air to escape: Air pockets can cause overheating because there will not be enough coolant in the cooling system, even if the radiator and coolant reservoir look full.
Add a mixture of one-half water and one-half antifreeze to the radiator. Fill it right up to the top.
Fill the overflow/coolant reservoir with the same 50/50 mixture.
Leave the radiator cap off, turn the engine on and let it run until the radiator "burps": You will see the coolant level drop and may see or hear a large air bubble come to the top as the system burps.
Keep an eye on the temperature gauge throughout this process.
Refill the radiator to the top and coolant reservoir as needed.
Put the radiator cap back on.
Note that if the engine runs hot after this procedure there may have been another pocket of air that "burped." Let the engine cool down and then add more coolant to both the radiator and the coolant reservoir.
Your cooling system will need to be burped after coolant has been drained from the radiator or any other part of the cooling system. Always dispose of coolant properly - do not pour it down the drain or sewer. Many service stations, repair shops and parts stores will take coolant so that it can be recycled, or you can bring it to a recycling center yourself.
Never open the radiator cap when the engine is hot! The radiator is under pressure, and it could spurt out and burn you. German and Swedish cars have plastic coolant reservoir tanks that are also pressurized - you must wait for the engine to cool down before opening the cap. Never let the temperature gauge go into the red - turn the engine off before the car overheats!