Dynamic checkout buttons are additional checkout buttons that send the customer to the Checkout page when clicked. These buttons appear as unbranded (Buy it now) or branded (Buy with [payment provider]).
Dynamic checkout buttons are largely controlled by the Shopify platform. Check out their documentation on the feature for more information.
Once you have determined whether this feature is right for your store, you can enable/disable the setting in the theme editor to activate/deactivate the buttons.