PromQL is a functional query language utilized for selecting and aggregating time series data in real time, commonly used for creating dashboards and alerts within the Prometheus monitoring system. The training session attended by the author covered the fundamentals of the time series data model, metric types, and both basic and advanced querying techniques, emphasizing the importance of understanding Prometheus' data model, which stores all data as time series. PromQL differs from SQL in that it is a nested functional language, with expressions evaluating to intermediary values and supporting two query types: instant and range queries. Advanced querying involves working with histograms, filtering, and using set operators to correlate time series data. Instrumentation best practices were also discussed, highlighting two guidelines—the USE Method for resources and the RED Method for request-handling services—as well as Prometheus-specific practices. Additionally, PromQL is instrumental in writing alerts, and Prometheus provides alerting best practices that can be explored further through recommended talks and documentation.