A nice picture for "how mountains formed" on Earth is due to the motion of tectonic plates. As the plates crash together, mountains may get "pushed upwards". However, a quick look at a map of the tectonic plates on Earth will show that there are some clear examples of significant mountain ranges which do not lie along the tectonic plates. I noticed the Ural mountains first, but even the Appalachian mountains don't appear to be associated with a particular pair of tectonic plates.
Nevertheless, Wikipedia tells me that the Ural mountains formed by the collision of the Laraussa and Kazakhstania continents - so why is there not a plate boundary underneath the Ural mountains?
EDIT: Here are few links with tectonic plate maps, demonstrating that there is no known division between plates at the location of the Ural mountains. Of course, I can't independently verify these, I'm just relying on consistency of unknown sources.
https://www.thoughtco.com/map-of-tectonic-plates-and-their-boundaries-1441098 https://pubs.usgs.gov/gip/99/pdf/gip99_ppt.pdf https://www.learner.org/interactives/dynamicearth/tectonicsmap/ https://earthobservatory.nasa.gov/Features/Tectonics/