Web hosting service is basically a space on the web where you websites front end lies. If you have a website, it needs to be on the web these service providers put your website on their servers and display it to the users whenever somebody goes to your URL.
There are two types of web hosting services. Some web hosting services will build your website and host it on their servers and another just host your own made website on their server. Depending on your business model you can choose either of the two options.