If your car is overheating even when it has engine coolant in it the problem could be caused by a number of different things.
Most commonly though a car overheating even with coolant is caused by a stuck thermostat that stays stuck closed and doesn't allow the coolant to flow through the engine properly.
Other causes could be a engine cooling fan not running when it should or a water pump that is failing to pump the coolant through the engine properly.
Another cause it a clogged radiator or clogged radiator hoses.
If your cars engine is overheating and it has coolant it should be checked out by a mechanic before it causes severe engine damage and possibly leaves you stranded.