Your domain name (like yourbusiness.com) is the address people type; DNS is the phone book that tells browsers which server to load. To put your site live, your domain has to point at our server.
If we register the domain for you: there is nothing to do; we handle it end to end.
If you already own the domain: we need either (a) login access to your registrar (GoDaddy, Namecheap, etc.) so we can point it, or (b) you add the DNS records we send you. We will give you the exact records - usually one or two lines to paste in.
DNS changes can take a few minutes to a few hours to take effect everywhere. We always verify the site loads over HTTPS before calling a launch done.