Functions are relations that only have one output per input (or graphically passes the vertical line test). You can either go on Desmos and graph this or just look at my explanations below.
1) function, pretty much all polynomials will be a normal function
2) function. This is a rational function, meaning you'll have some weird gaps and lines going to infinity but it's still a function. It's formed by a polynomial divided by another polynomial.
3) function, looks like you can simplify this into a standard rational function.
4) relation, y with an even square root are never going to give you a single solution (due to the nature of a + or - answer; = +3 and -3)