Rose: For cube beginners, I like to think of a person who doubles as saying "Hey, I think I can win the game - would you like to make the game worth twice as much?"

Then the opponenet can then either say (Accept) "I think I still have a good chance to win also, sure lets make the game worth twice as much and continue to play.

or the opponenet can say (reject) "I think you are right and will win the game also. I will give you this game and lets move on to the next" (with the value of the game at the cube value before the double offer)

At least that is the basics of it. As you play, there are many other little tips and tricks which will help as you play on. (Like if you think you are going to win with a gammon/backgammon, you should not double - or if it is past the crawford round and your opponent is 1 point away you should always double right away, etc..... things which will help your game, but not as important to learn how to start using the cube.)