Add

            public void Add()
            {
                int RandNo = 0;
                if (Rear < MaxSize - 1)
                {
                    RandNo = Rnd.Next(0, 26);
                    Rear++;
                    Contents[Rear] = Convert.ToChar(65 + RandNo).ToString();
                }
            }

Generates a new random number, converts it to it's corresponding Unicode/ASCII (not sure which encoding format) character and then appends it to the end of the queue. Note if the queue is full then then this method essentially does nothing.