How do I make menus like these?

So I'm looking at slickdeals.net and amazon.com, and I found something very intriguing. It's basic for most of you guys out there, but it's new to me. For slickdeals.net, when you click login, a login box pops up like so. Also for Amazon.com, when you hover over the left navigational 开发者_如何学编程menus, a new menu pops up! I think it's JavaScript, but how does this work? How can I do something like that?

Update:

Thanks for the answers! One more question about Amazon's website. I've been looking at it with firebug. So how are they making their sub menu appear? I was expecting the mouseover to change the sub menu from display:none; to display: block; but this isn't the case. What is it change on the mouseover to make it appear?

Looks like a combination of CSS and Javascript. Look into JQuery and JQuery UI. It's easy to use and has things that make sites like theses easier to develop.

Look into the UI stuff for the menus and drop-downs and things like that. That JQuery UI is really cool and lets you make really dynamic web pages. They have examples on the JQuery UI site that you can look at.

You can view source to find these answers for yourself. It appears slickdeals.net is using jQuery for its javascript effects.

http://jquery.com/