Prometheus-Basics is a newbie's introduction to this tool. It covers what Prometheus is, the tool's architecture, types of metrics and contains a walkthrough of how to get it configured.
This primer on Prometheus walks through installation, configuration and metrics collection.
Monitoring synchronous Python web apps with Prometheus and its asynchronous monitoring counterpart are two tutorials that show how to add middleware to your web apps that allows Prometheus metrics collection.
Monitor your applications with Prometheus is a getting started guide with a walkthrough of how to instrument a simple Golang application.
Custom Application Metrics with Django, Prometheus, and Kubernetes
shows how to handle the initial configuration with
deploys the Django web app using
Helm and configures Prometheus to scrape metrics
from the application running on Kubernetes.
A gentle introduction to the wonderful world of metrics has a quick summary that compares Prometheus with Nagios, then digs into the logging format and what you can visualize with this tool.
From Graphite to Prometheus explains some of the differences between using a StatsD / Graphite monitoring stack and Prometheus, such as how Prometheus scrapes data instead of the applications pushing data to a metrics aggregator, and the query languages for each tool.