Ideally, if you've written clean, beautiful, well-tabbed, organized, modern "web standard" code, your site will be "valid" — meaning it is free from errors that might throw the browser into "quirks mode" where you don't know how your site will display.
Go to each site, click on the "By Direct Input" tab, select and copy your code (HTML or CSS), then paste it into the field. Click check. Scroll down to see any errors.
This hot dog site is mostly clean except for a weirdness with the Google Web Fonts, but will likely be difficult for you to understand what the Validator is saying. Don't worry about that. The important point here is to realize it is worth learning to code HTML, CSS and JS well because it's much harder to clean up your code later than to simply write it correctly in the first place. And when you find a bug (or error), the validator is a good place to start investigating the issue.
It's a good idea to develop on a web server rather than by letting the browser translate your pages directly. A web server more closely reflects how your web page will be delivered online to a viewer. It can also be accessed from other computers on your network, which is useful for testing.
If you're feeling pretty comfortable, try this out. It assumes your project folder is on the Desktop.
Note: If you don't have a Mac, or you don't have Python installed on your PC, this may not work.
If you later want to exit this command, hit CONTROL-C to stop your web server.
This is great for testing and working, but to make the a website live, it has to (1) have a URL and (2) live on a web server. This is a computer connected to the Internet and running special software.
The details of web hosting are beyond the scope of this tutorial, but most hosting comes with space on a computer for your files to live and help registering a domain name (URL). Here are a few hosting services that are inexpensive, don't try to sell you services you don't need, and have great customer service.