The gundams are an enhanced version of regular mobile suits, which are giant human-like war machines that walk on two legs, and have two arms. All mobile suits either carry a gun, a light-saber type device, or other weapon of destruction, and are heavely armored. The years range far into the future, in the early 2000's, and technology has advanced enough for colonies to be created in space. These colonies have defense systems, and are like little domes that look just like Earth on the inside. Well, the problem is, these colonies are at war. The Gundam boys are caught up in the war, and begin defending the colonies.
On Earth, the World Federation was created to control the planet. Under the influence of OZ, a secret military organization within the Federation, the Federation began to build up its military forces and take over the colonies. Within the colonies, people began to fight back.
Thus, the colonies launched Operation Meteor. Each of the colonies built a Gundam Mobile-Suit, called this because they're made from a rare and freakishly strong alloy called gundanium, and sent it to Earth to destroy OZ. They were made to look like meteors entering the Earth's atmoshpere, so OZ would not suspect anything. Piloting these Gundams are the 5 teenage boys mentioned earlier: Heero, Duo, Quatre, Trowa, and WuFei.
There, on Earth, all hell breaks loose...on an important mission from the scientists who built the gundams, Heero Yuy and the other gundam pilots were sent to an OZ convention with the knowledge that all the head officers of OZ would be arriving there there via spaceship. Heero was ordered to destroy that spaceship.
What the gundam boys didn't know was that Treize, a highly ranked OZ officer, had set a trap for the boys, and instead of sending all of the head officers of OZ, he called for the head officers of the Earth Alliance. Sadly. Heero was not aware of this. Accidentally, Heero sliced through the ship like a hot knife through butter. Finally, he realizes what he has done, and travels to each of the family members of the victims, seeking their verdict.
From there, Trowa goes undercover into OZ, while the other gundam boys are busied with personal affairs. The fate of the Colonies is in their hands, the hands of young, ruthless warriors, and online time can tell the fate off the future.