Those two parentheses denote the method and hold instructions on what should happen. For instance:
<SCRIPT LANGUAGE=”javascript”>
document.write(‘<FONT COLOR=green>Green Text</FONT>’)
</SCRIPT>

That script will produce this: Green Text
See what’s happening? The document is being acted upon by the method “write.” Inside the ( and the ) is what should be written to the page. In this case, green text.