Put-in is usually near Pirdi, downstream from Kullu - operators bundle transport in the price. Check that your operator provides a helmet and properly fitted life jacket, not just a life jacket; several budget operators skip helmets on the mellower stretches.
The Beas rises at Beas Kund near Rohtang Pass and, per Rigvedic reference as the Vipasha (meaning 'freed from bonds'), is associated with the sage Vyasa, traditional author of the Mahabharata. The river also marks a significant point in world history: Alexander the Great's army mutinied on its banks in 326 BCE, refusing to march further east, forcing him to turn back and mark the easternmost limit of his campaign with commemorative altars. Today the roughly 20 km stretch between Pirdi and Jhiri near Kullu, downstream of Manali, is used for commercial white-water rafting through its Class II-III rapids.