Metering your audio correctly is a core skill that every producer needs, and there's much more to it than simply understanding that spending too long in the red is generally a bad idea. In this video from the course Audio Concepts 203: Advanced Metering, Joe Albano runs you through the fundamentals of level metering standards - what they are and how they work, and all in under 5 minutes.
Joe goes over a little history of mixing and mastering - the loudness wars, and how technology has changed since the analog era, allowing digital producers to squeeze their tracks much harder. He then explains that though there is still no single standard, universally-agreed scale to measure relative loudness, there do exist a range of standards that are in common use, and that you may have seen represented on your DAW's mixer, or in specific plugins.
He details why these exist, and in subsequent videos in the course, gives a complete and comprehensive guide to the various different forms of metering used in music production, and how best to use and understand them. Check out the course using the links below to learn all about how it works!