Gathering all kinds of telemetry data is key to operating reliable distributed systems at scale. Once you have set up your monitoring systems and recorded all relevant data, the challenge becomes to make sense of it and extract valuable information, like: Are we fulfilling our SLA? How did our query response times change with the last update? Statistics is the art of extracting information from data. In this tutorial, we address the basic statistical knowledge that helps you in your daily work as a system operator. We will cover probabilistic models, summarizing distributions with mean values, quantiles, and histograms and their relations. Advanced topics like time series forecasting and scalability analysis will also be touched. The tutorial focuses on practical aspects and will give you hands-on knowledge of how to handle, import, analyze, and visualize telemetry data with UNIX command line tools, gnuplot, and the iPython toolkit.