Any web site needs to be connected to the internet so that people can access it.  The most common way to do this is to put your web site files onto a web hosting providers computer.  The web hosts server computer is connected to the internet 24/7 (or should be!) and it 'serves' out your web site files (pages) to anyone who requests them on the internet.

A web hosting provider will have a number of server computers and each computer will hold the files for many web sites.  This is called 'shared hosting' as many web sites 'share' a server computer.