app/code/Magento/OfflinePayments/README.md
This module implements the payment methods which do not require interaction with a payment gateway (so called offline methods). These methods are the following:
Before installing this module, note that this module is dependent on the following modules:
Magento_StoreMagento_CatalogFor information about a module installation, see Enable or disable modules.
Extension developers can interact with the Magento_OfflinePayments module. For more information about the extension mechanism, see Plugins.
The dependency injection mechanism enables you to override the functionality of the Magento_OfflinePayments module.
A lot of functionality in the module is on JavaScript, use mixins to extend it.
This module introduces the following layouts in the view/frontend/layout directory:
checkout_index_indexmultishipping_checkout_billingFor more information about a layout, see the Layout documentation.