Well, my impression of a wireless NAS has been that of "a solution in search of a problem" but that's just me. You can certainly attach a USB hard disk drive to a Time Capsule or AirPort Extreme however, which provides a means of sharing files across your network. The device appears in the Finder under "shared" and otherwise behaves as if it is directly attached to your computer.
If I may anticipate your next question: how to configure Time Machine to back up this NAS device? The answer is simple, it can't. Time Machine is not designed to do that, but you can use other utilities such as Carbon Copy Cloner to perform scheduled backups.
In any event, since you are retired with presumably more time than money, to answer your initial question about a basic guide on the subject I would start by perusing Apple Support Communities contributor and resident Time Machine guru Pondini's comprehensive FAQ on the subject.
This specific question is addressed here: http://pondini.org/TM/2.html but there is a wealth of addition information to draw upon.
Pondini has done fantastic & expansive detailing of TM, which I admire no end, that being said, I think myself that it requires too much Rocket Science, & fails far too often, & can't be tested until you need it... in my mind, that it's not anywhere near a viable backup option... unless you're not aware of real backup options.