Saturated, Monounsaturated and Polyunsaturated Fats

My understanding until now was that saturated fats are unhealthy while polyunsaturated and monounsaturated fats are at least less unhealthy.

Recently I read that some saturated fats may be harmful while others may be healthy. The same is true of monounsaturated and polyunsaturated fats.

It's hard to know what to believe. And yet our health depends on it.