Here you can find our library of tutorials for learning all about STAC. You can find a list of even more tutorials from all over the web at the stac index.
If there's a topic you'd like to learn more about, we recommend joining our Gitter Chat. There may well be a blog post on the topic published somewhere on the web that one of our community can direct you toward.
We'll continue to add tutorials to the site bring new ways to learn and understand how to use STAC in the real world. If you'd like to contribute a tutorial of your own, we're acecepting pull requests to the stac-site repository.