Website drop down menu html?

Hello everyone. I'm workong on a website right now and I need help. At the top of the website I have Home, features, guestbook, contact me, photo gallery, etc. I just want to know how to give each of those things a drop down menu. For example, if someone puts there mouse over the features, I want a menu to drop down from there saying a bunch of features he can do. I just dont want my website to look over crowded with all of these things, it would look a lot better if it had drop down menus. If someone could give me the html code to do this and explain what to do, that would help me a lot. Thank you.