The "road" Frost is referring to is the paths you take in life. Paths like, whether you went to college or went travelling or had a hard childhood. In the second stanza, he says "Though as for that the passing there | Had worn them really about the same."
In the poem it's implied that the roads have the same ending. He doesn't want to go back down the road to the other one, because it goes to the same place. He thought this road might be better, because it was less traveled by, but by traveling it, he made it look the same as the other.
At the end, where he says "it makes all the difference," he's being ironic. In my opinion, what he actually means is, it doesn't matter which road you take. People take the more unique life path because they think it's better. People take the less unique because they think it's easier. But in the end, the paths are the same, and none of it matters. Your choices and life events all add up, but at the end of the road, all of us die, and end in the same place.
