If the leak is relatively small, doesn’t cause the engine to overheat, and doesn’t in any way contaminate your oil, then you can get away with driving on it for a little while. And depending on what caused the leak, you may be able to fix it yourself.
Radiator leaks are usually caused by a radiator cap malfunction, a broken or disconnected hose, radiator corrosion, or a header tank leak. If the leak is due to a broken or disconnected hose, you should be able to patch or repair the shoe yourself—sometimes it can be as simple as tightening the clamps on one of the hoses. For any other kind of leak, though, you’ll need to have a professional handle the repair.