How an order book sets the price
Participants post bids and asks at chosen prices and sizes. The best bid and best ask define the spread, and your market order eats through the book from the best price outward. Depth is literally the list of orders waiting.
Prices come from people deciding what they will accept. Nobody is obliged to quote, so a quiet market can have a wide spread or no quote at all.
How an AMM sets the price
A constant-product pool holds reserves of two tokens and prices every trade so the product of the reserves stays constant after the fee. There are no orders and no counterparty with an opinion — just a curve and whatever is in the pool.
This guarantees a quote at any size, which is the great advantage, and guarantees that large trades get progressively worse prices, which is price impact.
What each one costs you
On an order book you pay the spread and any taker fee, and you can be filled at several prices as you consume depth. On an AMM you pay the pool fee plus price impact determined by your size against the reserves.
For small trades on a deep pool the AMM is usually cheaper and always available. For very large trades a deep order book can be far better, which is why size matters more than venue branding.
Why liquidity providers behave differently
An order-book maker chooses prices and can cancel. An AMM liquidity provider cannot — the curve keeps quoting as the market moves, so the pool systematically sells the asset that is rising and buys the one that is falling. That is the mechanism behind impermanent loss.
FBT Swap routes across AMM pools on each supported network and across Solana aggregators. The quote you see already includes the pool fee and the measured price impact for your size.