Can someone please just give me an example of how ArrayLists are used in types programs that most people use regularly?

I'm sure there is a persistence layer of some kind. SQL, NoSql or some other kind of database. The ArrayList, or any other data structure, takes the relational data from the database and maps it into a structure that can be used as needed.

For example, let's say you had a make of a car; an Honda Accord for instance. There are several trims for that car, LE, SE, Sport Edition etc. In a database you would have a table for the Car, the Trims, and then a lookup table to map the Cars to the Trims. Well, when you need to display these in a browser, or in a client running on the machine, you need some way to programatically display any number of cars and there associated trims. So you would end with a Map (ArrayList, LinkedList etc) like so:

[
  "Honda Accord" : [
     "LE",
     "SE",
     "Sport Edition",
   ],
   "Other Car": [
      "Trim 1",
      "Trim 2",
      "Trim 3",
   ]
   // n number cars
]

In this way you can have 1 or n + 1 cars in the ArrayList and your code does not have to change. It just pulls from the database, maps the DB query to this array, and your done. You just loop through the list and display the contents:

for (String[] carTrims : cars) {
  for (String carTrim : carTrims) {
    System.out.print(carTrim );
  }
}

It's been awhile since I've used Java so forgive any syntax issues here.

Hopefully that helps.

-Ben