I feel like I'm missing something not in the sense of not understanding how to use the language but not fully understanding what the principles of functional pr

I feel like I'm missing something not in the sense of not understanding how to use the language but not fully understanding what the principles of functional programming are. At least, what makes one language imperative vs functional? I always thought functional languages were about describing what things should do whereas imperative languages were about telling the computer what to do. I suppose in that sense loops are not really functional because they are not very descriptive, but I was wondering if there was more to it than that.