From the Wikipedia page 
Butter, milk, and salt are added to brewed tea and churned to form a hot drink called Po cha (bod ja, where bod means Tibetan and ja tea) in Tibet. The concoction is also sometimes called cha su mar, mainly in Kham, or Eastern Tibet. Traditionally, the drink is made with a domestic brick tea and dri's milk (a dri is the female of the animal whose male is called yak), then mixed in a churn for several minutes. Using a generic black tea, milk and butter, and shaking or blending work well too, although the unique taste of yak milk is difficult to replicate. (see recipe )
Tibet tea drinking has many rules. One such concerns an invitation to a house for tea. The host will first pour some highland barley wine. The guest must dip his finger in the wine and flick some away. This will be done three times to represent respect for the Buddha, Dharma, and Sangha. The cup will then be refilled two more times and on the last time it must be emptied or the host will be insulted. After this the host will present a gift of butter tea to the guest, who will accept it without touching the rim of the bowl. The guest will then pour a glass for himself, and must finish the glass or be seen as rude.
There are two main teas that go with the tea culture. The teas are butter tea and sweet milk tea. These two teas are only found in Tibet. Other teas that the Tibetans enjoy are boiled black teas. There are many tea shops in Tibet selling these teas, which travelers often take for their main hydration source.