For some reason, I tried to drag the Applications stack onto my desktop, but when I did it disappeared! I went to the Finder and tried to drag Applications from the sidebar to the area of the dock for stacks, but my finger slipped on the mouse and I accidentally dropped it onto my desktop, where it promptly disappeared as well. Now it's gone from the sidebar in the Finder. How do I get things back to the way they were? Sorry if this is a silly problem/question, I only got my Mac a few weeks ago and I'm still adjusting!