The short version is that saturated fats generally have a negative effect on cholesterol, and the recommendation is to limit your intake. They’re popular because they’re found in many animal products, and have useful properties (such as often being solid at room temperature, like butter)
Then unsaturated fats are pretty much the opposite, whether poly or mono unsaturated. They have a generally positive effect on health. Use these when possible.
Most sources of fats are a blend of the different types, so don’t worry excessive about it.
Oh and then trans fats are the worst for you by far and are banned from sale in many places, although you can actually create them in your own kitchen I believe via some methods of deep frying