to make a variable that stores user inputted text you create

let mut guess = String::new()

then you call

io::stdin()
        .read_line(&mut guess)
        .expect("Failed to read line");

.read_line(&mut guess) calls the read_line method on the standard input handle to get input from the user.

&mut guess is a mutable reference to your string guess

read_line() returns a Result which is an enum indicating that if the process of reading contained errors or not. and it has expect() method to display a message on failure