The magic behind Juju is a collection of software components called Charms. They contain all the instructions necessary for deploying and configuring cloud-based services. The charms publicly available in the online Charm Store represent the distilled DevOps knowledge of experts. If you cannot find what you're looking for or if what's available does not suit your needs then you are free to write your own.
Charms make it easy to reliably and repeatedly deploy services. The Juju walkthrough is a quick-start guide that provides a practical overview of using Juju.
Generally, you follow a simple three-step procedure: deploy, configure, and expose services. The sub-sections in the left navigation pane under Juju Charms explore in detail this procedure as well the everyday operations you are likely to perform as you work with Juju Charms.