You'll see the option to geo-target your campaigns within the targeting section of your Twitter Ads interface when creating a new campaign or editing an existing one.
Type the country, state, metro area or zip code you'd like to target in the search bar.
A person above is right. It's the way to target a specific location. But if you don't know a zip code of a region you need then visit this site https://worldpostalcode.com/what-is-my-zip-code. One click and you get information about it. There are not only US codes actually. So it's pretty handy.