Good question this! The answer to both is because we all have different genes and different experiences.
We know there are genes involved in hair colour, eye colour, height, weight and facial structure. Depending on which versions of the genes you get from your parents, you can differ in all of these. Because you get a blend of genes from your mum and dad, its not surprising the we generally look a bit like one or the other of them.
Since identical twins have exactly the same genes, they look very much alike. But they are not *completely* identical. This is where experience and environment comes in. Identical twins might eat different foods, so the may have slightly different weights. One may be more sporty than the other as a child, so could have developed differently or one may spend more time in the sun, which could cause differences in skin tone.
The similarity of identical twins tells us looks are highly genetic, but they don’t act exactly the same all the time. This is because genes have less influence over how we act and experience has more of an effect. Genes still influence our behaviour, but they are harder to study because the influence is smaller.