What is the difference between String and str in Rust?

Hi! I just started learning Rust and got confused between `String` and `str`. In other languages, like Python or JavaScript, strings are just strings, but here it's some kind of zoo. I wrote this code: ```rust fn main() { let greeting = "Hello"; // Is this str? let name = String::from("World"); // And this is String? println!("{} {}", greeting, name); // Tried to modify greeting // greeting.push_str("!"); // Error! // But name can be modified name.push_str("!"); // Works println!("{}", name); } ``` I understand that `String` can be modified, but `str` cannot. But why? When to use which type? And what is `&str`? I've seen that functions often write `&str`, but I don't understand why. Also I noticed that `str` does not have a known