The quick answer
The difference is where the shiny foil sits. On a Holo card, the foil is behind the Pokémon artwork — the picture shimmers. On a Reverse Holo, it's the opposite: everything shines except the artwork — the card's borders and text box sparkle while the picture stays flat. A Non-Holo (also called a 'regular' card) has no foil at all. Tilt the card under a light and it's obvious in a second.
Holo (Holofoil)
A Holo card has a reflective, shimmering finish behind the main artwork. Historically these were the prized 'Holo Rares' — one shiny card per booster pack. The foil is part of what makes vintage holos like the Base Set Charizard so iconic. As of the Scarlet & Violet era, every Rare (black star) card is holographic by default, so 'holo' is now the standard look for rares rather than a special tier.
Reverse Holo (Parallel foil)
A Reverse Holo flips the shine: the artwork is normal, but the rest of the card — frame, text box, and background — is foil. Officially called 'Parallel foil,' these started in the early 2000s and exist for almost any rarity: there are reverse-holo Commons, Uncommons, and Rares. That's a key point — a reverse-holo Common is still a Common; the foil is a finish, not a higher rarity. They're popular with collectors who build 'reverse holo master sets' (every card in its reverse-holo version).
Non-Holo
A Non-Holo card has a flat, matte finish with no foil anywhere. Most Commons and Uncommons come this way, and plenty of older Rares were non-holo too. Nothing wrong with them — they're the bulk of any collection and perfect for filling out a Living Pokédex or a type/color page.
Does it affect value?
Usually, yes — at the same rarity, holo and reverse-holo versions typically sell for a bit more than their plain counterparts because they're scarcer and look better. But finish is only one factor; the Pokémon, the set, the artwork, and condition matter far more. A reverse-holo Common won't be valuable just for being foil. For a card's actual worth, check its rarity symbol and current price.
Displaying and protecting them
Foil cards show fingerprints and scratch more easily than matte ones, so handle holos by the edges and sleeve the ones you care about. In a binder, side-loading 9-pocket pages keep foils flat and scratch-free while letting the shine show — which is exactly why holo and reverse-holo cards make such satisfying display pages.