Candlestick and long wicks

Can someone explain what happens when the wick dips way low (or high) off the candlestick?

In this example, I get that the bottom of the wick is the lowest price for that time period that was bought/sold. But what causes such a crazy long wick? Seems like a trading signal I should be paying attention to but I'm not sure what do with the information.

That means somebody was taking all the sell orders.
He was buying for higher price. same happens if it goes red like that, that means somebody is taking all buy orders ans selling for lower price.

That means the price dropped all the way there but it didn't close there and quickly went back up. Not sure if that's what you're asking.

You can look up "whipsaw" regarding markets, i'm not sure the example you gave is quite extreme enough to meet the definition though.