Here's what I originally thought:
Twins Dipper and Mabel were sent by their parents to look for something in the woods, when they got kidnapped by a man named Stan who went by the nickname Uncle Stan (the commercial said "Uncle," not "Grunkle") who wasn't really their uncle, he just went by that. He took them to Gravity Falls and forced them to live in the Mystery Shack. They met Soos, Wendy, and others, along with many, many monsters.
What did you originally think the show was going to be?