The short answer is, get to a mechanic to determine the cause. The real problem is you have a potential for overheating which could ultimately lead to warped cylinder heads if left unrepaired. Often a radiator or coolant leak is caught earlier enough to prevent this type of major repair from being necessary. However, any leak on your car should be addressed. I can guarantee you that it won’t go away by itself and it will not heal itself. Fixing a small leak is far less expensive than fixing a leak that has been ignored.
It is important to fix any leak associated with coolant because it keeps your “car” cool. You can have a leak because of a poorly sealed radiator cap, a hole in the radiator due to age or something flying up and hitting it while driving. Sometimes the Radiator simply corrodes and rusts over time and can run out of coolant or even seep for a period of time. Coolant can also leak from one of the hoses, a clamp that broke, a line that popped off or rusted through, etc. Generally you have either metal and/or partly rubber lines your fluid flows through. Either way, metal corrodes and deteriorates and rubber simply breaks down. Some of that is accelerated by our winter weather, salt, etc.
I’m sure you have heard about a product called “Stop Leak.” It works well for the intended purpose. But, one of the problems is that it goes into every little hole even the ones you don’t want plugged. Stop Leak can cause overheating which leads you down the road of more repairs. So, use cautiously and only to limp you to the actual corrective repair.
It is important to maintain the right amount of coolant (antifreeze) as well as the right type. Your radiator is a closed, pressurized system which keeps the engine running at optimum temperature all the time. If there is a leak, the coolant gets low and creates expansion as the engine gets hot. This is why fixing a small leak is important. As the coolant gets dangerously low especially for an extended period of time, it can warp the heads and damage other parts of the engine.
Another leak can occur at the Heater Core which mostly happens due to a lack of antifreeze in the system. The antifreeze acts as a coolant in the summer as well. Of course, the water pump can also leak at the seal, which also deteriorates. The water pump is an item that is often replaced as general maintenance on a vehicle with higher mileage. However, you would not replace it unless there was a problem.
Remember never to remove a radiator cap when the car has been driven. It absolutely has to be cold. Even if the cap feels cool enough, it does not mean that the pressure inside the radiator has subsided. You can still get badly burnt if you remove the cap before it is completely cooled.
It is a good habit to look at the ground when you back out of your parking spot (at home or on the road) and make sure that there are no leaks. Your air conditioning will leave some water on the ground. If you haven’t been running the air, there should not be any condensation. If you see a leak, then stop soon to identify the cause. That way you will be able to make an informed decision whether to fix it now or later.