To read an element from an ArrayList, call .get() with the index:
ArrayList<String> colors = new ArrayList<>();
colors.add("red");
colors.add("green");
colors.add("blue");
String first = colors.get(0); // "red"
String last = colors.get(2); // "blue"
Indices start at , just like arrays. If you pass an index that is negative or greater than or equal to the list's size, Java throws an IndexOutOfBoundsException at runtime.
Notice you cannot use square brackets like colors[0]. That syntax only works with arrays. For ArrayList, .get() is the only way to access an element by position.