From various places in your Studio, you get an important opportunity to describe your Component - for your own reference and if you ever share. Check out the Component Editor article to learn where.
The "Description" area for components uses Markdown. Markdown is a text-to-HTML conversion language. It's really powerful and pretty easy to use. Check out the markdown reference for how to use it.
(We've repurposed a quick reference from Adam Pritchard's Markdown cheatsheet.)