How can I watch movies offline on my Android tablet? How can I watch movies on my tablet (Asus Transformer tablet with Android 3.2) offline?

I recognize that this is a very basic question, however, I can not find any step-by-step instructions on this site or online. It is also not clear if any popular sites such as Netflix, Amazon, or Hulu support offline viewing. I think that it would be useful to have step-by-step instructions. 

If I had the tablet in my hands, I would probably be able to figure something out - even though it is a new device and my first experience with Android. However, my wife has taken it and the children on a trip, and would like to use it for entertainment on the flight home.
Android comes with a basic video player called "Movies", although it might not show in the application list for some devices. To use the built-in player, you need to use the Gallery or a file manager to invoke the Movies app on the movie file you want to play.

Alternatively there are many alternative movie players on the Market. Here are a few threads to get you started: 


MX Video Player
MoboPlayer
RockPlayer
QQPlayer
VPlayer