Here's the idea in one line. Your skin, hair and nails are always rebuilding themselves, and that work runs on nutrients. When you're short on them, the rebuilding doesn't run as smoothly.
Hair and nails are made mostly of keratin, a protein. Biotin is one of the vitamins your body uses in the process that supports normal hair, skin and nails. It's why biotin shows up in nearly every beauty supplement on the shelf.
Skin cells are replaced constantly, and that turnover depends on normal cell division. Vitamin B12 and folate both play a role there. Vitamin B6 and pantothenic acid support normal energy metabolism, the background work that keeps every tissue running.
None of this is flashy. It won't "reset" anything or turn back the clock. What it can do is make sure your body isn't missing the basic building support it needs, day after day, so your skin, hair and nails have what they need to look their best.