Here's a breakdown:

* The Collision: About 300 million years ago, the supercontinent Pangaea was forming. This involved the collision of the North American and African tectonic plates.

* Folding and Uplift: The tremendous force of the collision caused the rocks on the edge of the continents to buckle, fold, and uplift, creating the Appalachian mountain range.

* Erosion: Over millions of years, erosion has worn down the peaks, giving the Appalachians their rounded, gentle slopes.

Important Note: While the collision was the main driving force, the process was complex and involved other geological events, including volcanic activity and faulting.