How is a linear queue structure different from a circular queue structure?

In a linear queue, insertion is at the rear and deletion is at the front, and once the rear reaches the last position no more elements can be added even if the front positions have become empty after deletions, so that space is wasted. In a circular queue the last position is connected back to the first position, so rear can wrap around and reuse the vacated positions at the front; the space is used efficiently.