There are three major settings in Tuck Everlasting: the woods adjoining the Foster property, the Foster home, and the Tuck home. All three properties are located in the rural town of Treegap.
The woods are important because of a very special spring located at the foot of an immense ash tree in the middle of the woods. The spring is the focus of the story because it affords eternal life to anyone who drinks its waters.
Meanwhile, the Foster home is important because the main protagonist, Winnie Foster, lives there. The Tuck home is significant because it houses the entire Tuck family: they are the only ones (aside from the man in the yellow suit and Winnie) who know that the magical spring arrests the aging process. This means that, if someone drinks the spring water at the age of twenty, he/she will stay twenty years old forever. The Tuck family consists of Jesse; his brother, Miles; his mother, Mae; and his father, Angus.
In the story, the author contrasts the two homes in order to make a point. While Winnie lives in a home that is "squeaking clean, mopped and swept and scoured into limp submission," the Tucks live in charming disorder. Winnie's home has a "touch-me-not appearance," and it is "enclosed by a capable iron fence.
In contrast, the Tucks live in a "homely little house beside the pond." Winnie knows that she was unhappy living a rigidly structured life, but it's the only life she's ever known. However, in the Tuck home, she discovers another way of living, and she finds peace amidst the comfortable clutter. In essence, Winnie discovers that there is more to life than following a set of rules. She comes to realize that she must make choices of her own.
Thus, the contrasting settings represent a metaphor for Winnie's dilemma: will she drink the spring water (and live an immortal, unconventional life) or will she continue to live the life she's always lived (and die of old age one day)? Also, the contrast in homes allow us to consider whether an ordered life is superior to a less structured one.
So, the contrast in settings highlights the themes of immortality and of appearance versus authenticity. Winnie has to decide whether she will live an unusual life at Jesse's side or whether she will live the life she's always known. Eventually, Winnie decides to choose mortality over immortality, and according to Tuck in the Epilogue, the choice was a good one.