Leaving aside the complicated history, in the United States, Hallowe'en is pretty simple. 1) Children, ages 3 to 15, perhaps, dress up in costumes and go around door-to-door. They knock on the door, say "Trick or treat!" The homeowner gives them candy. They say "Thank you," and "Happy Hallowe'en" and go on to the next door.
Hallowe'en has a kind of theme having to do with death and the macabre, but it isn't taken seriously. It isn't religious, and it isn't patriotic. Some people, maybe one house in ten, make displays on their lawn with skeletons, ghosts, and tombstones.
Popular costume themes include ghosts, witches, skeletons, and zombies. However, children dress up as all kinds of things: Star Wars characters, princesses, dragons, anything.
Themes of the season include pumpkins, a kind of orange-colored gourd or squash about 15 cm. in diameter. The pumpkins are hollowed out, holes are cut in them to represent eyes, nose, and mouth, and a light it put inside to make a "jack o' lantern." The seasonal colors are orange and black. The inside of the pumpkin can be cooked and made into a kind of dessert called "pumpkin pie."
You can look up the history--Hallowe'en is short for All Hallow's Eve, which is the night before All Saint's Day--but we don't really pay much attention to that. It's just witches on broomsticks, pumpkins, skeletons, and kids going from house to house trick-or-treating.
P.S. in the 1950s I learned to spell "Hallowe'en" with an apostrophe. I really shouldn't. Nobody spells it that way any more, it's just "Halloween."