Large companies and universities host their own web sites. The server is located on their own premisses and they have permanent 24 hour-a-day high-capacity telephone connections to the Internet Backbone.
This is far too expensive a solution for the vast majority of companies. The answer is to use an Internet Service Provider (ISP). The machine running your site is on their premisses and they provide the permanent high-capacity connection to the Internet. That machine is configured to provide a number of 'Virtual Servers', so that each machine can host a number of different sites. You do not need any equipment whatsoever at your own premisses, and the ISP's charge reasonable fees for hosting your site.
You do not even need to own a computer, although without one you won't be able to visit your own site!
Somewhat more expensive is 'Co-location'. In this case you buy the machine that will be used as your web server, but it is located at the Service Provider's premisses and is set up and maintained by them. With this solution there are no restrictions whatsoever on how you use the server and may well be a good solution if you need a large searchable database on your web site. This way you will have unlimited web space and no restrictions on Server tasks. Unlike web hosting, the machine will only be serving your web site.
A third solution is to rent a dedicated server from your ISP. As with co-location you're site will have sole use of the machine and you will be free to run whatever software you require on the machine, but the ISP will normally provide maintenance, back-ups etc.