HTML Code for drop down menu?

[Jakub03]

Would anyone be able to help me with figuring out the HTML code for the drop down menu?
I would add it to side bar so all the forum pages can be accessed easily so it would be something like the menu bar on this site http://forumserver.twoplustwo.com/1/two-plus-two/

Here is an example

Category 1

Forum 1 = www.link1.com
Forum 2 = www.link2.com
Forum 3 = www.link3.com

Category 2

Forum 4 = www.link4.com
Forum 5 = www.link4.com
Forum 6 = www.link6.com