You are studying jquery. It's a framework of javascript. Learning jquery is not the same a s learning javascript. But there is nothing wrong with jquery.
For starters this:
$('ul.files_menu').slideDown('
medium');
No medium speed use "slow", "normal", "fast" or the actual time in milliseconds.
To control the opacity use fadeIn or fadeOut
ex:
Code:
<script type='text/javascript' src='javascript/jquery.js'></script>
<script type="text/javascript">
$(document).ready(function () {
$('#button').mouseenter(function () {
$('img.filesfade').fadeOut();
});
$('#button').mouseleave(function () {
$('img.filesfade').fadeIn();
});
});
</script>
<button id="button">PUSH</button><br />
<img border="2" class="filesfade" src="images/6.png">
Again no fastmedium. use the same speeds given above.
Good place to learn basic jq is here
http://www.w3schools.com/jquery/default.asp