The first pyramids children are usually exposed to are the three in Giza, Egypt Their history books might also include a few pictures of Aztec and Mayan pyramids as well. Yet those only represent a small fraction of all the pyramids worldwide.
In Egypt there have been 118 to 138 discovered depending on reports. Sudan surpasses that with about 230 although theirs were much smaller in scale. In Mesoamerica where the Mayans and Aztecs were there were nearly 100,000 pyramids. Mesoamerica covered the territory that is now Belize, Guatemala El Salvador, Honduras and Mexico. There are around 100 in China. There are dozens scattered through out Europe including 16 in Greece and three large ones in Bosnia.
The Great Pyramid of Egypt in Giza was long thought to be the largest worldwide at 147 meters or 482 feet. The largest of the three in Bosnia called the Bosnian Pyramid of the Sun surpasses that at 220 meters or 721 feet. One of the largest found in Mesoamerica was the Aztec Pyramid of the Sun in Teotihuacan, Mexico which is 75 meters or 246 feet high.
However they are all dwarfed by the White Pyramid of Xian in China which was estimated around 1000 feet or 304 meters. That pyramid was last photographed in 1947 by a U.S. aviator but the Chinese denied its existence. To this day outsiders have rarely been allowed into the country to investigate the 16 pyramids of Xian.
The purpose of the pyramids varied in use but many of the cultures used them as tombs. They were also used as places of worship. To a degree some were used for storage. It has also been discovered in recent years that the Great Pyramid of Egypt and the Bosnian Pyramid of the Sun were used to as power stations. There are also theories that the placement of the pyramids at their locations worldwide helps balance the planet as it rotates.