New Relic is an application performance monitoring tool that allows users to monitor key metrics of their applications in production. It works by installing language-specific agents that collect data on code execution times, errors, and system resource usage. The agents send this data to New Relic's cloud platform once per minute, where it is organized and calculations are performed to show metrics on application performance, server resource usage, browser performance, and availability on dashboards and mobile apps. The New Relic dashboard provides visualizations of metrics like response times, Apdex scores, throughput, errors, and more to help users analyze the health and usage of their applications in real-time.