1. Sitting duck
The intersection is dangerous the pedestrians don’t have the traffic light in order to see.
2. Chicken
The subject is afraid of heights, which is why the subject is afraid of climbing up high places.
3. Night Owl
Ben stays up late, which allows him to easily watch the meteor shower. Since Ben has been staying up late all his life, he can use that as an advantage to watch the meteor shower, which also takes place late at night.
4 is just using all of these expressions in a paragraph (4 sentences minimum) to demonstrate the meaning and your understanding of the listed expressions.
For example, one of your sentences could be something like this:
Jack would be sitting duck if his mother hadn’t found him while he was lost in the woods.