You can use the inbound web service process to receive a request from and send a response to an external application, via an inbound web service. To manage the inbound web service process, set up an inbound web service action.
For a general overview of the:
Inbound web service process when run directly, refer to Inbound web service process.
Asynchronous inbound web service process, refer to Inbound web service process - Asynchronous.