The Mongols are an ethnic group that originated in what is now Mongolia, Russia, and China. Mongols descended from the Huns, which was also the origin of the Turks. Mongolian originated ethnic groups are Hazaras in Afghanistan and minorities in Europe.
According to Chinese historical records, Mongols descended from the single lineage of Xianbei, who was defeated by Xiongnu. However, Mongols are a different ethnic group from the Chinese.
They lived on the continent of Asia but they didn’t live in one spot. They were nomadic people that traded with the Chinese and Persians. They would set up tents when they stopped in an area. The tents were made out of felt, cone shaped, and called steppes.
What Countries Did They Live In?
Many, including Mongolia, China, Japan, Iran and Russia.
By 1279 the Mongol Empire had expanded to its farthest point going from Moscow, Russia to the South China Sea.
By 1294 the Mongol Empire had broken into four separate khanates or regions, each ruled by their own khan. To the north west was the Golden Horde, to the south west was the ll-khanate,in the center was Chagatai Khanate, to the east was the Yuan Dynasty or Great Khanate.
What did their buildings look like?
Mongolians lived in dwellings called yurts, which are round and had a collapsible wooden frame covered in felt made from sheep's wool, somewhat like tepees used by North American Indians. Yurts had to be portable easy to take down or put up because Mongols were a nomadic people, meaning that they had to move around often to find crops for their animals. The most important Mongols, like the khan and his top generals, had larger yurts than the other Mongols, often with decorated fabrics and even wheels.
In the later years of the Mongol Empire, when the conquests of new territories had slowed down, the Mongols began building permanent cities and towns for the first time. The most famous city was Karakorum on the Orkhon River, which was famous for having religious buildings for all major faiths and for its magnificent palaces.
What did they eat?
During the Mongolian Empire there were two different groups of food, “white foods” and “red foods”. “White foods” were usually dairy products and were the main food source during the summer. The main dairy product that Mongols lived on during the summer was “Koumiss” or fermented mare’s milk which is still widely drunk today. The Mongolians rarely drank milk fresh but often used it to create other foods, including cheese and yoghurt. “Red foods” were usually meat and were the main food source during the winter. Any time meat was served in the Empire it was usually boiled and served with wild garlic or onions.
What did they wear?
The boys and girls wore the same clothes, a del. This is like a dress that they wrap around themselves. Boys' dels are shorter than girls'. They sewed fur in their clothes to keep them warm.
They wore leather boots. They also wore hats and head-dresses all year round. Some were made of sable and others were made of silver fox for cold weather and in the summertime the hats were made of colorful fabrics. They made hats for special occasions too. They love hats. 
What did their writing look like?
Mongolian writing was based on the older Uyghur script, which was used by the Uyghur Empire which controlled Mongolia during the 8th and 9th Centuries. It is written vertically from top to bottom, left to right. Mongolian script was first used by Uyghur scribes under Genghis Khan around the year 1204. In China, the Mongols tried to copy the Chinese emperors who had ruled before them, and began writing in Chinese, using the Chinese characters. Mongolian script is still used to write Mongolian today in the Chinese region of Inner Mongolia, but not in the country of Mongolia today, where it was replaced by a Cyrillic alphabet similar to Russian.
What did they believe?
The earlier Mongol tribes mostly followed a type of religion known as Shamanism, where a shaman is a person who is believed to be able to contact and speak to the spirit world. One religion like this was Tengriism, which believes in multiple gods, the chief of which is Tengri, the Sky-Father. Some of the other tribes followed Manichaeism, a religion which used to be followed by the Uyghur Empire from the 8th and 9th Centuries.
As the Mongol Empire grew, it encountered many more religions - in China, the Mongols encountered Buddhism and Taoism, while they learnt about Islam when they invaded modern-day Iran and Afghanistan. They also had a lot of contact with Christians, especially the Nestorian missionaries who often travelled far into the east. The Mongol khans originally followed Tengriism, but they were very tolerant of other religions and were often eager to learn about other faiths. After the Mongol Empire broke up into smaller khanates, the local khans began converting to other religions such as Islam or Buddhism.
Are some of them famous even today?
Genghis Khan and Kublai Khan, the first and last rulers of the Mongol Empire are known worldwide. Genghis Khan united the arguing Mongol tribes under one banner, calling himself the khagan meaning "khan of khans", and set about conquering new lands for their people. The Mongols had lived on the steppes, the barren infertile mountains of Mongolia and northern China for many years. They grazed animals for food and generally lived a nomadic life.
Genghis Khan rallied the troops into a formidable army, made up of mostly highly skilled horse archers who devastated the kingdoms of the Chinese and Persians. Khan was known for his cruelty, when in one Persian city, he killed every man, woman and child and had their skulls piled up into a great pyramid to warn others not to resist him. Khan's campaign stretched across the vast wastes of Asia, into China, and deep into the Persian empire, ending up (when succeeded by his son) at what is now modern Hungary. Thankfully for the Europeans, they were spared the Mongol invasion when the army disintegrated and the unified army began fighting amongst itself.
Kublai Khan was Genghis Khan's grandson, and he admired the Chinese so strongly that he changed some of the Mongol customs to appear more Chinese. He became famous in Europe after the Italian explorer Marco Polo travelled to Mongolia to meet him and wrote a famous book about his adventures in Mongolia.
What is left of them today?
The Mongolians currently number about 8.5 million and speak the Mongol language. There are approximately 2.7 million Mongols in Mongolia, 5 million Mongols living in Inner Mongolia which is in China, and 1 million Mongols live in Russia. Ethnic subgroups of Mongols are: Khalkhas, Daurs, Buryats, Evenks, Dorbots, Kalmyks, Oirats, Kazakhs, Chakhars, Tumeds, Ordoses, Bayad, Dariganga, Urianhai, Uzemchin and Zakhchin.
When did their civilization exist?
The Mongol Empire lasted from 1206, when Genghis Khan united the warring Mongol tribes and was named khagan, to 1368, when the Mongol-led Yuan Dynasty was overthrown by the Chinese-led Ming dynasty. After the Yuan Dynasty fell, the old Mongol Empire broke up into smaller khanates each with their own khan, which gradually became less Mongol and more like the local people instead. The Mongols who stayed in Mongolia, however, carried on in almost the same way they had lived when the Mongol Empire started.