A web host is somewhere to store your web files and database. This involves a quick-and-dirty explanation of how websites work, so here goes:
As you've probably noticed if your computer's desktop gets overcrowded, files on your computer need to be saved somewhere. A website is usually made out of files and a database, and those need to be saved somewhere too.
If you only save them on your computer, you're the only one who can get to them, so they need to be saved somewhere that has explicitly allowed contact to the internet. That's where a web host comes in.
Web hosts are companies like Amazon (their Amazon Web Services branch), BlueHost, GoDaddy, etc. that give you someplace to store all the files that make up your website, usually for a fee.
For the purposes of this tutorial, we're going to use one of two options, because they're both reliable and free (or at least, free for you).
If you need help evaluating web hosts, places like Lifehacker, Ars Technica, and PC Magazine regularly publish breakdowns of which services have good reputations and what you get for your money. A quick google should find you what you need.