Changing domains is not trivial after you have been somewhere a few years. DNS is the worldwide method of relating system names with IP addresses. For example, Awtrey. Com is much more memorable than 192.41.7.215 is. I can also change Awtrey.
Every domain name is made of parts delimited by periods.
When you came to this site the first time, the computer you are on contacted its DNS server. But that is only one kind of resolution. DNS resolves differently based on the type of data being sent. A address that lists the computers in my domain. All this explanation prepares you for the fact that you have to choose to either let your ISP handle your email and DNS or your webhost.