Roasting is the usual cooking method for the turkey at a contemporary Thanksgiving dinner.
A turkey is commonly seasoned, placed in a roasting pan, and cooked in an oven until the meat reaches a safe internal temperature. The dry heat browns the skin while cooking the bird through, producing the familiar centerpiece associated with the holiday meal. Some cooks add aromatics, butter, herbs, or a separate stuffing mixture.
Roasting became especially established as Thanksgiving developed into a large domestic feast. It is efficient for cooking one substantial bird and leaves the oven available for side dishes at different stages. Modern cooks may use convection ovens, covered roasters, or spatchcocking, but these are variations on oven roasting.
Smoking, frying, and grilling are also popular contemporary alternatives, especially for cooks seeking different textures or shorter cooking times. They are not the usual method implied by the question. Poaching and boiling can cook poultry, but they do not produce the browned skin and roasted flavor most associated with a Thanksgiving turkey.