Identification keys are often found in guide books about whatever type of organism you want to get to know, though there are interactive ones online as well. I’ve used keys to ID plants, fungi, lichens, animal bones, butterflies, minerals, etcetera. Many of the keys are arranged dichotomously, which means they will offer two choices, one of which will best describe what you are observing if you’re in the right spot. Here’s a simple illustrated one about sharks: