Butter tea is not only a daily tea for Tibetans, but also common among most Chinese minorities in southwestern China, the Bhutanese, and Buddhist minorities in India.  Especially at high altitudes like Tibet and the Himalaya region where it is often cold, hot butter tea is a good source of calorie , and to keep body warm and hydrated. 
While evidence of tea has been found in Tibet before the 10th century, it did not reach its nearly universal status until about the 13th century. 
Many of us might not be familiar with this savory yak buttery tea. It could be difficult to imagine its taste before you ever try it. Liz Clayton from Serious Eat describes the taste of Butter Tea,
"From the minute the savory concoction hits your lips, it confuses. Slightly astringent yet warm and buttery, you're initially warmed and then confused with butter and then confused again with black tea. The sting of salt is like having a drink of the ocean—which usually feels like a mistake. You get thirstier and thirstier, which is Po Cha's clever little game, and it may take a western palate hundreds of sips (or cups) to begin to make up their mind. Many never finish the first." 
Tea has integrated into different cultures around the world for over 1,500 years. Today tea is by far the 2nd most consumed beverage in the world. (1st is water) It almost became a trend to see newly opened tea shops around the corner everywhere.
The most common legend is that Shen Nong (literally means "Divine Farmer"), also known as inventor of agriculture and Chinese medicine, discovered tea by accident in 2737 BC.  One day when he was enjoying his water that was just boil. (He believed boiled water is safer to drink and also increase longevity) Suddenly, the leaves of a tea plant fell into his cup. He tried it and liked the resulting beverage so much that tea was born. 
Tea drinking was likely to begin during the Shang Dynasty (1600 BC–1046 BC) in Yunnan, China for medicinal purposes. The first recorded drinking of tea was dated back to the 10th century BC China. The first tea monograph was written by a Chinese writer, Lu Yu, during the Tang dynasty around 760 CE. The book was called The Classic of Tea ("Chajing" in Chinese) and it introduces tea drinking in ten chapters. 
Tea was first introduced to Portuguese priests and merchants in China during the 16th century CE. Catherine of Braganza (a Portuguese princess), wife of King Charles II of England, took the tea habit to Great Britain around 1660, but tea was not widely consumed in Britain until the 18th century. In the beginning, tea was a luxury item only for special occasions, such as religious festivals, wakes, and domestic work gatherings such as quiltings.
In Britain and Ireland, tea had become an everyday beverage for all levels of society by the late 19th century when Indian tea began to arrive Europe in large quantities.
Photo by nagualdesign
INGREDIENTS & PREPARATION
Traditionally, tea is made by boiling tea leaves in water for half a day, achieving a dark brown color. It is then strained and poured into a churn with fresh yak butter, yak milk, and salt. After churning and all ingredients are mixed well, it will be poured into a thermos bottle or kettle to serve the hot foamy tea in individual cups or small bowls.  Sometimes it is mixed with roasted barley/maize called Tsampa too.
Because the traditional recipe requires ingredients and tools are not available to most people, an alternative method of making butter tea is to boil water with black tea leaves(Pu-erh, Darjeeling, or Nigiri) and cow milk(or half&half), then strain and blend the mixture with cow butter, and salt.
OTHER NAMES: Po Cha (“Tibetan tea” in Tibetan), Cha Süma ("churned tea" in Tibetan), Su Cha (in Sherpa)
Tibetan Butter Tea is a hot tea made with yak butter, milk, salt, boiling water, and a special black tea brick that comes from Pemagul, Tibet.  The resulted tea has a purplish color.