Okay kiddo, once upon a time there were two kinds of DVDs that people could watch movies on: regular DVDs and high definition DVDs. These high definition DVDs were called HD-DVDs and Blu-rays.
Lots of companies wanted to make money by selling these high definition DVDs, so they made different kinds. Some companies picked HD-DVDs and other companies picked Blu-rays.
But instead of just letting people choose which one they wanted to buy, these companies wanted their kind of high definition DVD to be the only one people bought. So they started a war to see who would win and make the most money.
People who wanted to buy high definition DVDs had to choose between HD-DVDs and Blu-rays. That made it confusing and some people didn't want to buy anything until the war was over and there was just one kind to choose from.
In the end, the Blu-ray format won the war. That means that people can only buy movies on Blu-ray now if they want to watch in high definition. But don't worry, regular DVDs still work just fine if you don't need the super high quality picture.