You can't drag items from the sidebar onto the dock -- dragging off the sidebar will make it disappear (just like dragging of the dock disappears an item).
Go the finder window and click on your hard drive icon. (or double-click the hard drive icon on your desktop).
Then drag your applications folder onto your dock (you can drag it back into the sidebar of your folder as well).
YEAH! What he said. I did this once too and was scared for a second (back when I was more of a noob, like yourself). Don't worry. Just remember, Apple keeps things simple, if something happens just think of what you'd want to do to fix it and try that. Keep It Simple Stupid.
Yeah, usually the fix is the most idiot proof method. Microsoft has made people think way too hard on how to correct problems.
If you just think of the most obvious way to fix it, you'll probably be right.