Web hosts are companies that provide space on a server they own for use by their clients as well as providing Internet connectivity, typically in a data center. Webhosts can also provide data center space and connectivity to the Internet for servers they do not own to be located in their data center, called colocation.

In short if you have a modern website you need a server for it to run on. Hosting is the rental cost of that server. Costs can range from a few pounds to hundereds each month, depending on the website of course.