Write a dialogue between the traveler (Frost) and a friend. The dialogue should explain his choice of road and where it led him.
The best advice that I can give you is to put yourself in the traveler's shoes. The poem says that he took the road that was less traveled. Perhaps because "it was grassy and wanted wear." Frost doesn't spell out the traveler's reasons for the reader. It's up to the reader, which works to your advantage, because you can write about whatever you feel like.
Friend: "Why did you take that road?"
Traveler: "Because . . . (pick a reason)." It looked cooler. I like being alone. Because I can't stand doing the trendy thing. I heard fairies in the forest in that direction. Pick something. It doesn't matter based on the prompt that you have been given.
The second part of your prompt asks you to explain to your friend where that road not taken led you. You can answer it in a very literal, straight forward manner. "It took me to a clearing." That's totally fine, but you are going to need to explain to your friend why taking that road that led to that clearing made all the difference.
Frost seems to indicate that taking the less traveled road created some kind of life changing event. What Frost doesn't indicate is if the event was positive or not. Taking the less traveled road might have begun a series of horrible events. You could write about those and have your dialogue with your friend taking place years later. It's up to you to determine what you want to write about, but I think that you will have more fun if you choose a dialogue sequence that doesn't play into the poem's standard nice, "fuzzy" feelings.