this is what those end up being, it's pretty straightforward?

    fn five() -> i32 {
        return 5;
    }

    fn five() -> i32 {
        5;
        return ();
    }

semicolon changes the expression from returning the result of the expression to running the expression and returning the unit type. if you accidentally do that and specified a non-unit-return-type in the function signature, the type checker tells you about it:

    error[E0308]: mismatched types
     --> src/main.rs:1:14
      |
    1 | fn test() -> i32 {
      |    ----      ^^^ expected `i32`, found `()`
      |    |
      |    implicitly returns `()` as its body has no tail or `return` expression
    2 |     5;
      |      - help: remove this semicolon to return this value

which is also pretty clear about the solution