This phrase is used here to mark the beginning of a new part of the story. If your language has a way for doing this, you could consider using it here.
The word "behold" alerts us to the introduction of the dead man into the story. Your language may have a way of doing this. English uses "There was a dead man who was...”
## the city gate ##
This could also be translated as "the entrance to the city."
## an only son to his mother ##
"a woman's only son"
## widow ##
This is a woman whose husband has died.
## was deeply moved with compassion for her ##
"felt very sorry for her"
## and coming forward ##
Some languages would say "and going forward" or "and approaching the group."
## funeral couch ##
This was a stretcher or bed used to move the body to the burial place. It did not have to be something the body was buried in.
## I say to you ##
Jesus said this to emphasize his authority. It means "Listen to me!"
## the dead man ##
"the man who had been dead." The man was not still dead; he was alive.