Update queue readme (#4721)

Author: AnujRathour

src/main/java/com/thealgorithms/datastructures/queues/README.md

@@ -31,17 +31,58 @@
 - **Delay Queue:** Used for scheduling tasks to run after a specific delay or at a certain time. Elements are removed from the queue when their delay expires.
 
 ## Declaration
-
-`Queue<Obj> queue = new PriorityQueue<Obj> ();` 
+`Queue<Obj> queue = new PriorityQueue<Obj>();`
 
 ## Important operations
 
-| Operations | Description |
-| ----------- | ----------- |
-|Enqueue|Adds an item to the queue|
-|Dequeue|Removes an item from the queue|
-|Front|Gets the front item from the queue|
-|Rear|Gets the last item from the queue|
+| Operations | Description |Time Complexity
+| ----------- | ----------- |-----------
+|Enqueue|Adds an item to the queue|O(1)
+|Dequeue|Removes an item from the queue|O(1)
+|Front|Gets the front item from the queue|O(1)
+|Rear|Gets the last item from the queue|O(n)
+
+## Enqueue
+ It adds  an item to the rear of the queue.
+
+ For example: If we have `1, 2, 3, 4, 5` in queue, and if we call Enqueue(8),
+
+`8` will be added to last index of queue -> `1, 2, 3, 4, 5, 8`.
+## Dequeue
+ 
+ It removes an item to the front of the queue.
+ 
+ For example: If we have `1, 2, 3, 4, 5` in queue, and we call Dequeue(),
+
+`1` will be removed from front of queue and returned -> `2, 3, 4, 5`.
+
+## Front 
+  It returns an item to the front of the queue.
+
+For example: If we have `1, 2, 3, 5` in queue, and we call Front(),
+
+`1` will be returned (without removing it from the queue).
+
+## Rear
+  It returns an item to the rear of the queue.
+  
+  For example: If we have `1, 2, 3, 5` in queue, and we call Rear(),
+
+`5` will be returned (without removing it from the queue).
+
+# Real Life Applications
+`Task Scheduling in Operating Systems:`
+
+Processes in a multitasking system are often scheduled using queues. For example, the ready queue contains processes ready to be executed.
+
+`Multi-threaded Programming:`
+
+Queues are often used to facilitate communication and synchronization between different threads.
+
+`Breadth-First Search (BFS) in Graphs:`
+
+Queues are used in algorithms like BFS to explore a graph level by level.
+