Hello and welcome to COL
It sounds like your puppy is feeling a bit overwhelmed with the outside world at the moment. Driving to the park and sitting on a bench is a good idea. Take some treats and if he's happy to sit and watch the world go by, or play with a toy, or just have a sniff around, quietly praise and reward him for anything positive. If he's afraid of something try not to react to his fear by making a fuss because that may reinforce his fear.
I don't know if you're a first time dog owner or not, so apologies if this is something you already know, but don't assume that all other dogs will love him and be nice to him because he's a puppy. Many adult dogs tolerate puppies but some don't and some adults and puppies may be too rough if they play with him. So be careful when other dogs approach you or you approach them.
If your puppy is relaxed enough in the park try and do some training with him. While he's still so young he'll probably want to stay close to you so it's the right time to start training a solid recall in preparation for when he's a teenager and less likely to listen to you
. You can practice things like that at home and in the garden and then try them out in the park.
Would love to hear more about your boy. Is he a show type or worker and what's his name?