"The Road Not Taken," by Robert Frost, is available to read for free in the links below. Here is a short summary.
The narrator of the poem stands at a fork in the road, where the path "diverges in a yellow wood." He looks down both paths, wondering which one to take, and is sorry that he cannot take both to enjoy both experiences. He looks down one path as far as he can before it curves and he can't see farther. At this point, he makes the decision to take the other path, which is "grassy and want[s] wear," as it is the path that most travelers avoid. He does note, however, that the paths look about the same from this perspective. As he walks, he ponders that both paths are covered in leaves that "no traveler has trodden black," meaning that both paths have been unused for a while, and wonders if he can ever return to take the other path; he realizes that every choice he makes leads to another choice, and he will probably never return. Continuing, he confirms to himself that even if he remembers this story with regret, it is a choice that he made without coercion, and his choice of "the road less traveled" will "make all the difference" in his future life.
The poem is often seen as an allegory for the choices made in life, where a person can choose one of two equally valid (positive or negative) options. Frost comments that to choose the "less traveled" option is to avoid some of the routine and sameness that many people experience.