Answer :
They were the first American expedition to cross what is now the western portion of the United States.
They went on an expedition to explore the west, which was the Louisiana Territory, where others were already exploring. What made them unique was they explored the Oregon Territory and were some of the first men to travel across the entire "country". They had a crew and were assisted by Sacagawea, who traveled with her son on her back for most of the trip. One of thier goals was to find a waterway that connected the east and the west, at first the thought it was the Missouri River. But it ended up being a series of rivers. (They started in Pittsburgh.) And followed the Missouri River to the Yellowstone River, to the Snake River and finally the Columbia River which led them to the Pacific.
Hope this helps! I was born in the North West and they're kinda a big deal there. (: There are forts you can go to where they stayed, and follow their trail. It is actually pretty cool.
