What was Pangaea? Why does it no longer exist? What happened?

Pangaea is the "super continent" that existed approximately 175 million years ago, this super continent was made up of every land mass you see on a modern day globe but it was all together, not broke up like it is now.
An example of this is if you've ever looked at a globe and thought "South America looks like it would fit together with Africa" well it looks like it would because at one point it was part of Africa.
The reason that the continent broke apart and are still separating is due to Continental Shift where the Earth is sitting on top of molten rock which causes the crust of the Earth to move ever so slightly. On average the North American continent moves about 2-3 inches closer to the Asian continent every year! at the current rate of travel of the continents they will all be joined together again in "Pangea Ultima" and that's just 250 million years from now.