MQTT, or Message Queuing Telemetry Transport, is a messaging protocol designed to efficiently transmit data between devices and applications in IoT systems. It operates on the client-server model, where clients communicate with a central server, the MQTT broker, which routes messages based on topic structure. Key concepts include topics, quality of service (QoS) levels, retained messages, last will and testament, and session persistence. Node-RED is an open-source visual programming tool that allows users to create flows by wiring together nodes to perform tasks visually and intuitively. MQTT nodes in Node-RED facilitate communication using the MQTT protocol, enabling interaction with MQTT brokers, publishing messages to topics, and subscribing to topics to receive messages. By combining MQTT with Node-RED, developers can build practical applications in IoT, automation, real-time data processing, home automation, industrial IoT, environmental monitoring, energy management, agriculture, security, and surveillance.