Please explain Robert Frost's poem "The Road Not Taken," line by line.

The poem begins with the speaker saying that he is in the woods, at a fork in the road: "Two roads diverged in a yellow wood" (line 1).  He feels regret that he cannot, as just one person, take both roads: "And sorry I could not travel both / And be one traveler" (2-3).  So, he says that he stood there for a while "And looked down one as far as [he] could / To where it bent in the undergrowth" (4-5).  He followed the first road with his eyes as far as he could until he bent away into the forest.

Next, he looked at the other road, saying, "Then took the other, as just as fair" (6).  The second road is just as fair, just as pretty as the first, though it might, perhaps, be somewhat more desirable a path ("having perhaps the better claim" (7)) "Because it was grassy and wanted wear" (8).  In other words, the second road is grassier than the first.  However, he says, "Though as for that the passing there / Had worn them really about the same" (9-10).  This means that about the same number of people seem to have taken each road; they are each worn about the same amount (by the passing of feet) as the other.

And on this particular morning of his travels, the two roads "equally lay / In leaves no step had trodden black" (11-12).  No one had yet taken one of these roads today, and the leaves that cover them are untouched by anyone else's feet.  The speaker decides to take the second, grassier road, saying, "Oh, I kept the first for another day!" (13).  And he knows that he'll probably never get a chance to come back and try the first road: "Yet knowing how way leads on to way, / I doubted if I should ever come back" (14-15).  One road will lead to another, will lead to another, and he'll probably never be at this same fork in the road again.

Finally, he considers what he will say, many years from now when he tells this story: "I shall be telling this with a sigh / Somewhere ages and ages hence" (16-17).  He plans to say that "Two roads diverged in a wood, and I— / I took the one less traveled by, / And that has made all the difference" (18-20).  In other words, he will tell people that, when he came to a fork in the road, he took the road that fewer people had taken.  However, we know that this will be a lie because he has already said that about the same number of people have taken each road and that they lay "equally" that morning.  The speaker, then, will lie and tell people that taking the road less traveled has made a big difference in his life, that it has impacted his life in some significant way, but this is not true because there is no road less traveled.

In the poem, the roads are symbolic of any decision that a person might make.  We often have choices, and we like to believe that those choices are unique and that they make a big difference in our lives.  However, this poem implies that such a belief is really only a fantasy, that there are no unique decisions because they've all been taken about the same number of times by others who came before us on these "roads."