What is the difference between let and var in Swift?

Hi! I just started learning Swift and can't understand the difference between `let` and `var`. They both seem to be used for declaring variables, but I noticed that Xcode sometimes complains if I use the wrong one. For example, I wrote this code: ```swift var name = "Ivan" name = "Petr" // works let age = 25 age = 30 // error! Cannot assign to value: 'age' is a 'let' constant ``` Why does the first case work fine, but the second gives an error? I thought `let` and `var` were the same thing. Maybe `let` can't be changed at all? But then why is it needed? I also noticed that in examples from the internet, they often use `let` for arrays and dictionaries, but then add elements to them. How does that work? Doesn't `let` forbid changes? Please explain in simple terms, wha