A server controlling an external device is provided. The server includes a communicator; a processor; a memory which stores at least one natural language understanding (NLU) engine for generating a command corresponding to a user's utterance. The server receives, from a pairing device paired to the external device, the user's utterance controlling the external device and information about at least one external device registered with the pairing device, via the communicator, determines an NLU engine corresponding to the external device, from among the at least one NLU engine, based on the user's utterance controlling the external device and the information about the at least one external device, and generates the command controlling the external device based on the user's utterance, by using the determined NLU engine.