How can we grow an array in a circular buffer / circular queue implementation

Question

I'm trying to learn about the implementation of a circular queue using arrays, and currently, my main source of learning how it works is through this page.

https://www.happycoders.eu/algorithms/implement-deque-using-array/

However, I'm struggling to understand how one method in the code works, and that is the growToNewCapacity() method. I've provided the code down below.

public class ArrayDeque<E> {
        private static final int DEFAULT_INITIAL_CAPACITY = 10;
        private Object[] elements;
        private int headIndex;
        private int tailIndex;
        private int numberOfElements;

        public ArrayDeque() {
            this(DEFAULT_INITIAL_CAPACITY);
        }

        public ArrayDeque(int capacity) {
            if (capacity < 1) {
                throw new IllegalArgumentException("Capacity must be 1 or higher");
            }

            elements = new Object[capacity];
        }
    private void growToNewCapacity(int newCapacity) {
        Object[] newArray = new Object[newCapacity];
        int oldArrayLength = elements.length;
        int numberOfElementsAfterTail = oldArrayLength - tailIndex;
        System.arraycopy(elements, tailIndex, newArray, 0, numberOfElementsAfterTail);
        if (tailIndex > 0) {
            System.arraycopy(elements, 0, newArray, numberOfElementsAfterTail, tailIndex);
        }
        headIndex = 0;
        tailIndex = oldArrayLength;
        elements = newArray;
    }

I'm just completely lost after the second line of the method which states

Object[] newArray = new Object[newCapacity];
int oldArrayLength = elements.length;

Anything beyond that is completely dumbfounded for me, so can anyone please take some time off to explain what exactly is going on with the code, so that I could implement it based on my understanding later on.