Connecting an N600 router to an adsl modem

> How to connect an N600 router to an adsl modem ?

   Ethernet cable?

   "N600" is a speed, not a model number.  Ever helpful, Netgear product
packaging emphasizes speeds like "Nxxx", but that's not the model
identifier.  Look at the product label.

   "an adsl modem" is not a very detailed description of anything,
either.

   Is this a new installation, or are you adding equipment to an
existing installation, or what?  What, exactly, are you trying to do?
In any case you may need to supply some actual information before you'll
get much specific advice.

   For a Netgear device, visit http://netgear.com/support , put in your
model number, and look for Documentation.  Get the User Manual.  Read.