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.
Candid photos can be challenging because you might have to take a few to get just the right shot. You can’t really tell your subject to move into the right light, because the image would no longer be candid. Take your camera to a family gathering or a party and capture candid shots. Choose your best photo and describe the lighting challenge you faced and why the chosen image turned out so well.