All the code in this directory (and hence in the Automattic\WooCommerce\Internal namespace) is internal WooCommerce infrastructure code and not intended to be used by plugins. The important thing that this implies is that backwards compatibility of the public surface for classes in this namespace is not guaranteed in future releases of WooCommerce.
Therefore plugin developers should never use classes in this namespace directly in their code. See the README file for the src folder for more detailed guidance.