In less than 90 seconds, you can catch up on the Gears of War story.
So lets say you have a really, really, really busy life schedule and you have never played the first two Gears of War games, ever. Then, lets say you want to get into Gears of War 3 but don't have time to go through the two games campaigns which consists of giant worms, missing wives, and wave after wave of Locusts Horde coming for your blood. Well, if you got two minutes of your life to spare, then you can get caught up easily in the main meat of the story.
A world exclusive Gears of War short called "Dust to Dust" was released recently which speedily goes over the most important plot points of the Gears of War series and gets you straight to where the last stand of humanity is at right now. Sure it won't explain every single detail but it covers a lot in such a short amount of time, which is very impressive.
Think of it as a cliff notes version of Gears of War. If you want to understand the entire universe of GOW, then there are numerous sites out there you can read and get up to date on where the series stands now in full detail.