A web host is a company that has servers that are connected to the internet 24 / 7 /365

These servers are assigned unique IP numbers in order that they may be found by other computers connected to the internet.

It is on these servers that all your web files are stored.

The "Readers Digest" condensed version of what happens is, When you type a web address into the address bar of your browser and then hit Go, your browser sends out a request to 'get' that web page.

First your ISP's DNS server transalates the common name ( whatecer.com ) to the IP address of the server that houses the domain, then the request travels to the appropriate web server and attempts to locate the web page on that server.

If the request is successful (web page exists) then that web page will load (or download) into your web browser.