"down" has many different uses - it can be an adverb, adjective, preposition, verb, or noun depending on the situation In your example, "down" is being used as a preposition meaning: moving further along the course of something examples with the same use as yours: "he lived down the street" "I walked down the street" You can substitute "on" for "down" in "wandering down the street" but it does imply a bit of a different meaning - even so, most English speakers would know what you are trying to say Hope this made sense!

It means "to go" or "to move" by means of walking. Within your sentence it means that the person was walking down the street aimlessly with no destination in mind, no real purpose like someone who is lost, or a bum with no home, no job, no place to be. Most of us walk down a street with a purpose in mind (such as from home to school, etc.). And yes, the word "on" could be substituted with no change in meaning. I hope that this helps you. J.

Good question, it only changes the feel of the sentence. "wander down the streets" sounds more temporary, and could imply a destination "wander on the streets" sounds more permanent, maybe the person has nowhere else to go.\ Given context, the reader will understand either.