Behavior of the statement

(Display Figure 4.)

The program uses the value of the counter named index as a numeric index to locate a specific element in the array.

Then the program accesses the contents of that element.

In this case, that will be a specific penguin object. 

Having gained access to a specific penguin object, the program sets the opacity property value for that object to 100% with a time duration of one second.

This causes the penguin to become visible over a time span of one second.