A host is the service provider where your site resides and is served up to viewers to see. This requires the ability to send your information over an internet pipeline or “band”. Hosting can either be dedicated meaning that the servers on which your site resides is yours alone or it can be shared meaning that your site sits alongside other sites.
Think of it like a library. You might have a library with many books and many topics or conceivably you could have a library dedicated to one very prolific author. You can easily see how that would be terribly wasteful unless so many people wished to take out that authors books all at the same time. So like the library with many books as people need your book (or site) they access it through the shared host whose bandwidth is rarely over worked.
It is a good idea when starting out to use a shared host as it is very inexpensive and there is little downside in terms of speed for your site. Occasionally being on a dedicated server will increase site ranking with search engines but so many other factors contribute to ranking that this is fairly low on the SEO priority list.
Shared hosting can cost as little as $3.95 a month compared to some of the dedicated services that go up to hundreds or even thousands of dollars per month.
Importantly plans are available which allow the user to maintain unlimited numbers of sites on their shared hosting account for one moderately small fee per month (about $20). This is very useful if you intend to host many sites for the purpose of identifying which is best and which you want to put your energy against.