Enter the Library

1) >Insert >New Symbol

2) Give it a name and press OK.

That puts you in a new environment, the library.

3) Create your fish. Notice the little cross hair. That is the center of the library. Try to create the fish around the cross hair.

Adding Fish to Scene

4) After creating your fish, jump to scene1. Click on scene1 in the upper left corner.

5) >Window>Library
Click on fish2
Drag fish2 from the library window onto the stage.

6) >Insert >Layer
Name the layer fish2

7) Resize the fish by selecting the transform tool.
Select a corner of the fish.
Put your finger on the shift key to keep the dimensions.
Size the fish to your choosing and move it off the stage.
Follow the instructions for tweening to move the fish.
8) Save your work.