Token prices are set by the oracle, which allows all trades to be executed with a fixed price without any slippage. No matter what the order value is, be it just $1 or $100,000, the price will stay the same. As long as the contract has enough liquidity, the order will be fulfilled instantly.
Anyone can deposit funds into the smart contract and earn trading fees.
When you provide liquidity, you receive STL tokens which represent your stake in the pool (in percentage). Over time, as more and more trades are executed, the pool value and the value of your STL tokens grows.
You can redeem your STL tokens back into the stablecoins at any time. Note that the redemption (withdrawal) also bears the same fee as the normal swap. If this fee wasn't present, anyone could deposit one token into the contract and immediately withdraw it in another token for a swap without fees.
Head over to Stablecoinswap.io to use the frontend or interact with the smart contracts directly.