Although learning html has fallen out of fashion in recent years, I believe it is a skill that is important to know. Even if you'll never be a professional web developer, there are times when knowing a little html is beneficial. Today I stumbled across Mozilla Thimble.
It allows you to write html online in the left pain and immediately see the results in the right pane. Once you have completed your masterpiece you can post the page publicly and share the link for all to bask in your gloriousness. What's more, your masterpiece is available for others to use as a learning tool and remix.
Thimble is a part of Mozilla Webmaker a "global community dedicated to teaching digital skills and web literacy." If you don't know where to start, they have a ton of various projects that you can load directly into Thimble and use to learn html.