Bridge

The bridge is the piece of wood(usually) that keeps the strings up. It's in between the f-holes. recently, something happened to mine and it got crooked and my strings all went flat. I asked a friend, and I was told that it isn't uncommon for that to happen, and to just carefully push it back. It was pretty easy putting it back, too.

So if this somehow happens to you, push the part that the strings rest back to where it was, try to get a 90 degree angle with the violin. Be sure to tune after this.