Of course you can rent the dvds too, but it's nice to be able to watch episodes without waiting.
See the Netflix site for info on system requirements. You need a high speed connection, for one, of course. Can only view episodes, can't download (of course), but then it's included with your Netflix membership.
How many hours of online viewing you have per month depends on your Netflix subscription. If you can rent 3 dvds at a time, that's $17.99 before tax, and Netflix will allow you 18 hours of online viewing during your monthly billing cycle. (For instance, my cycle starts on the 23rd of the month, so if I've already watched 18 hours by the 15th of the month, I won't be able to view anything else via Netflix online until my cycle begins again on the 23rd.)
Online viewing has no effect whatever on your dvd rental queue.
Didn't see this posted here and thought some other Dick Van Dyke Show fans might like knowing this.
P.S. .. and yes, someday I do plan to get all the dvds. But meanwhile I have a kid in college. All in good time!