Websites are designed so that others can see them and in order for a website to be seen it must be on a computer which has continual access to the Internet. This is what hosting refers to.
You could provide your own hosting, but you would need to maintain the computer yourself and have a permanent connection to the Internet. This isn’t usually an issue for a large company or institution that has the staff to maintain such a set-up, but for most individuals and small to medium-sized companies it isn’t cost effective.
So in that case the best option is to find a company that specialises in hosting websites, that maintains its own computers that are connected to the Internet all the time. This is referred to as shared hosting, because there are hundreds, even thousands, of websites being hosted on one individual machine. Each of these areas on the hosting machine will be associated with a unique web address (URL), so that when you type that address in a browser, it goes directly to those files. Shared hosting is like renting a flat in a large apartment building!