Depending on your state and whether you live in a city, suburbs, or somewhere more rural the answer will vary.

Some places casual conversations with strangers is normal others people tend to ignore each other.

Regarding neighbors if you live somewhere with a yard or garden it's not uncommon to borrow or lend tools like a pressure washer or snowblower. You could also offer to help them do yard work. If you want to make a good impression I'd offer help before asking for it from them. (If you do borrow one make sure to return it in a timely manner)

You should also look to see if there are any local community events like your town celebrating the anniversary of it's founding.

If you go to a church, temple, or mosque you could probably ask there, they might have cook outs or other events.

The comments about volunteering seem really helpful. Go down to your local animal control center and you will meet some decent people.

Also, Halloween tends to create possibilities. Even if you are just handing out flyers for a local project of some sort.

I gather you are not going to bars, which is a really good idea

Try volunteering somewhere, you will likely meet good people that way. Usually you have to be decent to give up your time for the benefit of others. I volunteer at a local clinic and a "soup kitchen", made a lot of friends that way. If you want to be a part of the community you cant go wrong by helping solve the problems of the community. If you're not sure how to get started, check out your local United Way.

Learn jiu-jitsu or judo, you get to know everybody.

Are you in a city? The suburbs? A small town? Do you work with other people? Go to church or temple or mosque? To college?

As an adult I have made friends from work, from yoga, and oddly enough, Pokemon go. Not counting the friends who were parents of my kids' friends since that probably doesn't apply to your situation. But I am in a mid-sized city with a large contingent of people who were not born here. So many different people from different places.

Also if/when you get a girlfriend (or boyfriend, whatever applies) they may come with some built-in friends and family, will help expand your circle.

Work, groups, going to social events, etc.

I moved from the Midwest to the east coast after college. I found that the city I was living in didn't like people that weren't originally from there. The only friends I made were other people who didn't grow up there. And some of them were from like 45 minutes away, and they were still not wanted. I was never happier to move back to the Midwest.

So, maybe where you live just isn't receptive to newcomers?

Two words: Palestinian Chicken.

That’s the cool part. You don’t! ;)

New to America USA, how do you socialize and meet new people?

Carefully. Very carefully. They have guns and like to use them. Especially on people they don't know, don't like, who look strange, or who have an accent.