Don't be bashful! If you want comments, give comments. You don't need to be an expert photographer to express your opinion about the work of others. You don't need to go into great depth. A simple remark about cropping, composition, color, subject matter, etc. can be of just as much help to a budding photographer as an in-depth critique.
Your assignment is to take street photography. Find a location that allows you to be relatively unnoticed, yet able to view people as they go about their normal activities. You don’t want to use a flash, because it is distracting to your subjects and prevents you from getting the most candid shots. Choose a photo that displays interesting lighting conditions. For example, you might be able to get a silhouette of a person or show the sun or a street light hitting your subject’s face in an unusual way.