I learned all this great coding but I don't know where to put it on the internet. Any help is appreciated.
You have to set up a production server. There are companies like GoDaddy to get your domain name. Then you have to rent space on a server host. GOOGLE is a great tool. Look up how to set up public website, how to get a domain name, how to set up server on an host.
Some great references here: https://plus.google.com/u/0/b/106238285827137455054/+ProgrammingResources/about
Not to be cynical, but for a newbie the web is not a very friendly place. Our mistakes are never forgotten and if we are dependent upon search engines to deliver traffic, then we need to be fully aware of their guidelines and policies. Nothing is worse than having your home page end up in a supplemental index.
Better to find a sandbox where you can hone your skills, and where it does not bring any strokes against a production website. Also consider building a website on your own computer. There you can edit and revise and refine all you want without the world seeing it. When a search engine first finds and crawls your site, you don't want any errors in those pages. If that page gets indexed, it could be months before any repairs show up in the index.
Just 2 cents worth.
Like @mtf is suggesting, it's probably a better idea right now for you to code locally. Once you want a website though, GitHub Pages is a great free hosting service for static sites, and I've got a guide on setting GH Pages up here.
I think it makes great sense to be able to practice and setting everything up before going live. But how do I actually set up a sandbox, or build a 'secret' website just accessible from my own computer?
Thanks for your time!
You can always access local html files through the browser. But if you really want to test with a webserver, you can install apache. This (depending on your settings) is only accessible from your computer or computers in the network. If you are in your home network (which i assume you trust), that other computers in the local wifi can see your webserver isn't a problem (maybe even nice so you can test it on other computers
Many webservers run linux, not windows, so you could also install linux to get familiar with what you will be working with when you publish your webserver