Telegraf is a daemon that collects metrics from systems, services, and third-party APIs, and outputs them to InfluxDB and Kafka. It is plugin-driven, allowing for easy extension and modification of data collection and output. Telegraf was originally built for InfluxDB but has evolved to support other data sinks like Kafka, Datadog, and OpenTSDB. The guide covers installing and configuring Telegraf, running it on a system, viewing its data in Kafka and InfluxDB, and exploring additional features and plugins.