nighthawk ax5 router

> nighthawk ax5 router

   Not a model number.  Look for "Model" on the product label or
package.

> is a firewall required for the router to work, or connect to the
> internet?

   It's a router.  It needs some kind of connection to an Internet
service provider (ISP).  That typically involves some kind of modem or
optical network terminal (ONT).  A firewall is a different type of
gizmo.  A router has some firewall-like capabilities, itself.

   Visit http://netgear.com/support , put in some actual router model

number, and look for Documentation.  Get some.  Read?