Queue: Queue is a "first in, first out" (FIFO) data structure. It contains a pointer to the first node and last node, and its size.
Queue Node: It contains the data and a pointer to the next queue node. Its information is shown in a rectangle. The label below the rectangle shows the associated memory address
API Explanation:
1. Push Back: Add a new node at the end - O(1)
2. Pop Front: Remove the first node - O(1)
3. Clear Queue: Clear the entire queue