In simple words... when we enter the address of the site in the browser, we do not think about where the text, images and design come from. The page loads because somewhere is running a computer in whose memory files with the text of the site, pictures, videos, scripts are stored. This computer is called a server. Hosting - a paid service. It includes a rent of space on the server and its capacity.
 

Necessary no, but highly recommended.  Depends on how many people will visit your site and how much downtime you can afford.

Hosting is a paid service, but it's worth it. Hosting can also be done on your home computer, but then you have to keep it on around the clock and yourself to monitor the load and power outages. I use and am always satisfied with the quality here . I think it's better to pay for this service and take some of the worries off your hands.