Thanksgiving is a meal that was historically eaten just "when something good happens" according to the Puritans when they arrived on this shore. "Thank you God for what you have given us etc." It was a habit in England before any colonization happened.
Here, it eventually became almost synonymous with meals that happened after raids on Native American settlements and acquisition of their food stores.
It became an official once-yearly holiday in the time of Abraham Lincoln post-Civil war, a way to "bring the country back together." Unfortunately as I understand it the festival was declared a US holiday shortly before Lincoln sent US soldiers to once again attack the Sioux.
For these reasons a fairly bog-standard, politically neutral religious observance has become charged with imperialist and colonial overtones.
Usually people assemble for a meal of New World foods, such as mashed potatoes, peas, turkey, stuffing, baked sweet potato, corn, gravy, biscuits. Sometimes part of the ritual is taking turns going around the table and saying what you are thankful for this year. After a sensible pause pie is eaten, usually pumpkin or apple, although berry, sweet potato, and pecan pies are also popular.
Friendsgiving is a Thanksgiving meal that you hold with your friends, which is especially common in the GLBT community. It may not take place on the actual day of Thanksgiving. Because Americans who celebrate the Standard American (Christian) Holidays are usually required to spend Christmas with family, it's possible to have a gathering with your friends for Thanksgiving the month or so before and be correctly gendered, able to bring your partner, and so on. Friendsgiving has also become common with college students away from home, immigrant communities, and other young adults living apart from their parents.
Most people working white-collar jobs in the US do not work on Thanksgiving, but many minimum-wage workers are still required to come in. For this reason it is also common for Thanksgiving to be celebrated early or late in families with many working-class members.