The best things are free at Downtown Disney: You can stroll around, enjoy the scenery or listen to street performers. At around 9:30 PM you can catch the great fireworks display right from the district. The fireworks are launched above the sleeping beauty castle, but very prominent from several locations in the district.
Disneyland opened its doors to the public on July 18, 1955. Since then over 500 million people visited the park from all over the world. It is considered the most visited park in the world, second only to Disney World in Orlando, Florida. If you really want to know the history, go to Wikipedia.