In order to get this kind of stablecoins, users block a special cryptocurrency in the contract, which then issues a certain number of requested coins.
In the future, to return the collateral, users send stablecoins to the same contract for reverse currency exchange (taking into account various commissions or interest rates).
Algorithmic stablecoins are not pegged to fiat or cryptocurrency. Instead, price stability is achieved solely by algorithms and smart contracts that manage the delivery of the token issue.