This namespace should always be included since it contains the base classes and methods for Web API V3.
This namespace contains methods that are used internally to communicate with the Web API. You will most likely not need to use them.
Methods that are used to call the Web API 3. A detailed list is available at https://serialkeymanager.com/docs/api/v3. Each class contains a list of related methods that perform an action on a certain object. For example, the Key class contains the methods Activate(String, ActivateModel) and CreateKey(String, CreateKeyModel), and they are related since the affect a 'Key' object (LicenseKey in SKM Client API). If you want to change a customer object (Customer), such as AddCustomer(String, AddCustomerModel) or GetCustomerLicenses(String, GetCustomerLicensesModel), you would have to look into the CustomerMethods class.
All the classes that are either used as a paramter for an API method or represent the data that is being sent back.