I have never been to US or Canada so kinda keen to know how do people celebrate Thanksgiving. This occasion is pretty well-known cause almost in every TV this occasion has been used.
Why turkey is apple of eye in Thanksgiving???
In the United States, Thanksgiving is private and personal. We don't have parades or fireworks or anything like that. It is a family occasion. In the United States many people live in small "families" with a husband, a wife, and children. On Thanksgiving, extended families will get together. Sometimes, the grandparents will host the event, and their adult children will come with their families. There might be eight, twelve, twenty people getting together. The central event is a big meal.
The meal is often preceded by "saying grace," a prayer of thanks for food. Some families do this at every dinner; many do not, but will do it for special occasions like Thanksgiving. Sometimes, everyone around the table will be asked to name something they are thankful for.
There are well-established traditions for Thanksgiving food. There are variations, of course. The main course is usually a turkey... often a very large turkey. Common foods include baked beans, sweet potato casserole, cranberry sauce, cider, apple pie, and pumpkin pie. Many families have their own traditions for favorite food. Every Thanksgiving I've ever been to has included an argument between the people who like clear, smooth cranberry jelly out of a can, and people who like lumpy cranberry jelly with bits of chopped cranberries, orange, and orange peel in it.
Thanksgiving is connected to a cherished story, about 25% true and 75% myth, about "the first Thanksgiving" in 1621. The story tells how about an early British colony, in Plymouth, Massachusetts--"the Pilgrims"--who got together with the Indians (native Americans, Wampanoags) for a peaceful feast together.
A famous Norman Rockwell painting shows Thanksgiving as it might have been celebrated in the 1950s. It's wonderfully accurate.
https://www.strattonmagazine.com/wp-content/uploads/2017/11/Freedom-from-Want_HiRes_9med.jpg
In the United States, the reason why turkey is the main course is that the Thanksgiving dinner is supposed to be remembering "the first Thanksgiving" in 1621, and thus the foods that are eaten are supposed to be foods that might have been eaten in 1621. Turkeys are native to the United States. The national bird of the United States is the Bald Eagle, but Benjamin Franklin wanted it to be the turkey.
Nobody tries very hard to make the meal historically accurate, but the idea is there. Baked beans were common in the early days of the Puritans. Pumpkins, a kind of big orange gourd, would have existed. Most of us don't really eat pumpkin most of the year, but we eat pumpkin pie at Thanksgiving. Cranberries are a very, very tart fruit native to Massachusetts, where the first Thanksgiving took place, and so forth.