Obtain Domain
We are using namecheap for purchasing domain names and managing them via namecheap DNS. They provide excellent service along with good prices on domain names.
If you are not sure how to start, they have a great page explaining step by step a sensitive process of finding your perfect domain name.
https://www.namecheap.com/domains/domain-name-search/
P.S. the domain name is just a part of a complete stand-alone e-commerce website. It needs SSL and Hosting as well.