Make theme able to do Drop-Down menus

Alright, so this is the first time I’ve coded my own theme and I’m having a bit of trouble with having drop-down menus work on it – I wasn’t aware that this was something that I had to make the theme be able to do.
Anyway, so when I first tried adding a sub item when in appearance<menus and doing the indenting thing it would just add the sub category as a permanent link right under my main menu and shifting a bunch of content around.
So after looking around for a bit I ended up doing the following.

Adding this to my functions.php file:

//Register Custom Menu's
    register_nav_menus(
      array(
        'main' => 'main',
        'secondary' => 'secondary',
        )
      );

And this to the header.php file, before the closing header div:

<div id="menu" class="menu-center">
    <?php wp_nav_menu( array( 'theme_location' => 'main' ) ); ?>
</div>

And finally adding this CSS:

ul.menu,ul.menu ul,ul.menu li,ul.menu a {
display:block;
margin:0;
padding:0;
}

ul.menu ul {
display:none;
}
ul.menu li:hover {
z-index:999;
}
ul.menu li:hover > ul {
display:block;
position:absolute;
float:left;
}
ul.menu li {
float:left;
width:auto;
}
ul.menu ul li {
float:center;
width: 150px;
margin-left: -40px;
border-bottom:1px outset #a1a1a1;
}

ul.menu ul li ul {
float:left;
width:190px;
position:absolute;
left:100%;
top:0;
}
ul.menu-ver,ul.menu-ver ul {
width:14em;
}

div.menu-center ul.menu {
float:left;
position:relative;
left:50%;
}

div.menu-center ul.menu li {
position:relative;
left:-50%;
}

div.menu-center ul.menu li li {
left:auto;
}

ul.menu li a:link,ul.menu li a:hover,ul.menu li a:visited,ul.menu li a:active {
text-decoration:none;
}

ul.menu li {
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='white', endColorstr='#000000',GradientType=0 );
background: white;
}
.menu-center {
float:right;
margin-right:95px;
}

After all of that, it didn’t even end up making it a vertical drop down, but instead it’s going vertically.

You can see it on my site here: dinaxdesign.com

So my questions is 1) Is this even the right code to be using?
and 2) If not, then what is? If yes, then how can I make it go down vertically instead?

Thanks! I would really appreciate any help!!