Pieces you need:

 2 large rectangles

 2 arches

2 triangles 

2 semi-circles

1 play mat

2 small rectangles

Steps:

Step 1: Turn the playmat on its thin side into an L shape. Ensure one side of the L is facing where you want the audience to be.

Step 2: Place an arch on top of the front-facing side of the L. Place a rectangle on the other top of the L.

 Step 3: Set up the audience seats using the remaining pieces. Place an arch on top of the large rectangle. And the triangles on top of each small rectangle.

Step 4: Put people or stuffed animals on the seats and start the show.