When you are looking to host your website or web application, you have two options:
Register your domain name with your host and do nothing in particular except wait for the DNS to spread.
You have selected two providers: one for hosting and the other for the domain name. In this case, it is your responsibility to communicate to your registrar the name servers of your host so that your domain points to your hosting. For this purpose, in general, your host provides you with these name servers (in the form: ns1.example.ch, ns2.example.ch) and your registry gives you access to a panel allowing you to fill in a form with the addresses or ip of the servers provided.