c7000v2

> I just bought this per salesperson's recommendation. [...]

   Trust no one, I always say.

> [...] When I opened the box I realized it has a coax connector, [...]

   Typical for a cable-TV modem(+router).

> [...] I have dsl using an ethernet cable.

   What, exactly, does that mean?  Do you have a DSL modem(+router) of
some kind?  Which?

> [...] Can I plug into the ethernet socket or is that output only?

   "_the_ ethernet socket"?  The C7000v2 User Manual shows four.  Visit
http://netgear.com/support , put in your model number, and look for
Documentation.  Get the User Manual.  Look for "Rear Panel".

   The terms "input" and "output" don't really apply, but the Ethernet
ports on a C7000v2 are LAN ports, and you (probably) need a router with
a WAN Ethernet port.  In general, a cable-TV modem+router would not be a
good choice for a non-cable-TV service.

   Some Netgear _DSL_ modem+router models have a WAN/Internet Ethernet
port (which can be used instead of the DSL port); the D7000v1 is one
example.  I'm unaware of any Netgear cable-TV modem+router models which
do.

you got the wrong unit. It does not work with DSL ISPs.