The short answer is that "DNS" is the acronym for "Domain Name
Server", a computer in the network that takes the name (URL) that you
type into your browser and returns the numeric IP address assigned to
that name. The IP address is the "real" address of the place you want
to look at.
You don't set up a DNS; that's a job for your Internet service
provider (from your email address, presumably that's mobis.com). If
you can't contact a valid DNS, call their help desk for instructions.