Same here

What is actually this event? please
Basically, it's a day of celebration of all the things we have to be thankful for--and it's also a massive "eating fest". Typically whole families get together--mom, dad, siblings, aunts, uncles, cousins, grandparents, and assorted others and share a HUGE meal (those who can afford to do so). Americans excel at the eating part through the rest of the year as well; the part where we are thankful for all the great blessings we have seems to not come as easily to many of us.
After the English colonists came to America back in 1620, they set about trying to survive in this land that was so foreign to them at the time. Many of them didn't make it through the winter--but when planting season came, native Indians who were here before us helped the settlers learn how to plant crops that would grow in the native soil. The first Thanksgiving, then, was supposedly a sort of "first harvest" feast with the Indians and Pilgrims, as they gave thanks for life in this new land and for their Indian friends who'd helped them learn to survive and thrive.
Shortly thereafter (in the grand scheme of things), we pretty much turned on the Indians and things went downhill for them in a hurry. In the long run, they probably weren't all that thankful for having helping the "white man" to survive.
More about American Thanksgiving, if you're interested, is here:
http://www.history.com/topics/thanksgiving