How can I use a script to create users in MongoDB?

You can use createUser() method for this. Following is the syntax −

db.createUser(
   {
      user: "yourUserName",
      pwd: "yourPassword",
      roles: [ { role: "read", db: "yourDatabaseName" } ]
   }
);

Let us create a user in MongoDB. Here, we are using database ‘test’ −

> db.createUser(
...    {
...       user: "David",
...       pwd: "David123456",
...       roles: [ { role: "read", db: "test" } ]
...    }
... );

This will produce the following output −

Successfully added user: {
   "user" : "David",
   "roles" : [
      {
         "role" : "read",
         "db" : "test"
      }
   ]
}