The Alps are a long row of mountains dividing southern Europe from Northern Europe. They formed about 34 to 23 million years ago, when the African tectonic plate bumped into the European tectonic plate. As the two plates pushed on each other, they pushed a bunch of rocks up, just like when you push two piles of sand toward each other on the beach. There must have been lots of volcanoes erupting all over the place and huge earthquakes as this happened. But it didn't happen all at once. The plates only move less than nine centimeters a year, so the mountains would have taken millions of years to form.
Today the Alps are older mountains, and there are no longer any active volcanoes in the Alps, but they are still growing between a millimeter and a centimeter each year!