When you write a handler for a function, you specify statements that compute and return a value to the handler that calls the function. Each function handler has the following form, where the italicized words are placeholders:

```
function <i>functionName</i>
    <i>statements</i>
end <i>functionName</i>
```

HyperCard has many built-in functions, but you can also write your own:

```
on mouseUp
   put square(5) into the Message box
end mouseUp
function square x
   return (x * x)
end square
```

The function<code> square </code>receives a number through its parameter variable,<code> x</code>.  It then returns the value of<code>  x * x </code>to the handler that called it (<code>mouseUp</code>) using the<code> return </code>keyword.