Your puppy is going to see a lot of different things throughout their life! Creating positive associations with different sights while they're young can help prevent fear of unusual things in their environment later on. A dog's sense of sight is different than ours, so consider things from your puppy's point of view when socializing your puppy to different visual stimuli.
Often, dogs startle because of an unexpected appearance or movement of objects. If your puppy has ever encountered a statue, you might have seen them worried by the fact it wasn't moving as expected. You can help your puppy adjust to different sights in their environment by pairing the experience with a delicious treat.
Start at a distance where your puppy notices the new thing, but doesn't show any fear or stress. When they look at it, say "yes" (or click if you're clicker training), and give them a treat. Repeat as they look at the object.
If your puppy is comfortable, slowly approach the new object. Reward frequently for showing curiosity.
If your puppy shows any signs of fear or stress, such as tail tucked, ears back, or barking, add distance between them and the sight. Entice them away with a happy voice and treats. You can go back a few steps to a distance where they were comfortable looking at it, or simply end the session and put the object away.
Distance is your friend in this conditioning process! Manage the distance based on your puppy's pace. If they are cautious, don't force them closer or make them interact with the object. This can create a negative association with the new sight and create future fearful responses.
Check out the resources below for video examples of desensitizing your puppy to new and different sights and objects.