This poem by Robert Frost describes the dilemma a walker faces when the path he is treading diverges into "two roads." The two roads are, in fact, nearly identical.
The first one, as the speaker looks down it, takes a bend into the undergrowth of the forest, precluding him from seeing its end. The other was "just as fair." At first the speaker believes the second path is more attractive because it seems grassier, as if fewer people have walked upon it. Reconsidering, the speaker decides that, actually, they were about equally worn. Both of the roads were covered with leaves and relatively unsullied; they had not been "trodden black" by the feet of previous travelers. The speaker must choose one of the roads, and he doubts that he will have a chance to come back to this place and try the other one in the future. He makes his choice and selects the one "less traveled by," the second one, despite the fact that he previously concluded that both paths had been more or less equally used.
The poem, in one interpretation, is about indecision and making a mountain out of a molehill. The point was simply to take one path and move on, especially since there was no appreciable difference between the two ways. The final stanza can be taken sardonically; the fact that he chose one path over the other made "all the difference," but it is impossible to know what that difference was since the other path was "the road not taken."