Puppies are a huge investment with a small window of opportunity. From Birth until 12-16 weeks they are sponges capable of absorbing all kinds of information. If the experiences are wonderful to mildly stressful and the outcomes are rewarding. Your puppy will be having good “socialization” experiences.
If by contrast your puppy is fearful or having bad experiences these things will also be absorbed quickly and may create lasting phobias or behavior problems.
If you have a new puppy who is between the ages of 8 and 12 weeks, I STRONGLY encourage you to seek out a Reward-Based Puppy Class. There are two such wonderful puppy groups in San Francisco. I can recommend SMARTY PUP & SF PUPPY PREP with high regard.
If you have adopted an slightly older puppy (12 weeks -6mo), then you should give serious consideration to a Private Behavior Consult. Your puppy is TOO OLD for the basic advice given in most puppy books. Your puppy is entering its first fear-phase. Another one will follow at 8-10months. This is a critical time to be gentle and go slowly. Puppy books will recommend expansive exposure, but this is SPECIFICALLY for pups 8-12 weeks.