What Is Thanksgiving?

As an outsider to the American tradition of Thanksgiving, I had no idea what it is actually about.  All I know is that people usually eat turkey and pumpkins, so I did some research on this American festive holiday which will be taking place in America in three days time.

From Britannica Online Encyclopedia:

Thanksgiving Day, annual national holiday in the United States and Canada celebrating the harvest and other blessings of the past year. Americans generally believe that their Thanksgiving is modelled on a 1621 harvest feast shared by the English colonists (Pilgrims) of Plymouth and the Wampanoag Indians. The American holiday is particularly rich in legend and symbolism.

This still doesn't help me know what Thanksgiving is about, so I went on Thanks Much which stated:

For thousands of years, mankind has set aside a day each year to celebrate bountiful annual harvests. Before the establishment of formal religions, many ancient farmers believed that their crops contained spirits which caused the crops to grow and die. Many believed that these spirits would be released when the crops were harvested and they had to be destroyed or they would take revenge on the farmers who harvested them. Some of the harvest festivals celebrated the defeat of these spirits. Harvest festivals and Thanksgiving celebrations were held by the ancient Greeks, the Romans, the Hebrews, the Chinese, and the Egyptians.

If you are American or Canadian, what is Thanksgiving to you and what do you do to celebrate Thanksgiving?