Hi, @idkohli. There are a couple of different options. Which is best only you can say.
First, you don’t have to use Netlify DNS to host sites at Netlify using your domain. External DNS is always an options. You can keep your DNs service with your registrar and use these instructions instead:
However, you can also use Netlify DNS and point domains to other services. This would be the second option.
For example, I believe the Shopify DNS instructions can be found here:
They give instructions for making A records and CNAME records on the page above. You can follow those directions and create those records with Netlify DNS. This will point those domains to the Shopify site just like they will with any other DNS service. Netlify DNS will behave just like any other DNS service in this respect.
If you are having difficulty making DNS records, please let us know what records you are trying to make and we will send instructions for how to create them with our service.