How does getting a domain work?

There are two pieces to this equation. First, there are domain registries that own the individual top-level domains (like Verisign, which owns .com, .net, and a few other TLDs). Then there's us, the domain registrar, which provides a big online store that houses all the TLDs in one convenient location. When you register a domain, we reserve it for you through the individual registries... like an Amazon of sorts if you were looking for an HDMI cable.