Final answer:
Joseph's brothers sold him into slavery due to jealousy. This precipitated Joseph's eventual rise to power in Egypt and his family's subsequent move there.
Step-by-step explanation:
Based on the biblical account from the Book of Genesis, what Joseph's brothers did to him first out of jealousy was they sold him into slavery. This act was a result of their envy towards Joseph because of their father's favoritism towards him, which included gifting him a coat of many colors. Joseph's brothers stripped him of this coat and sold him to Ishmaelite traders who in turn sold him into slavery in Egypt. This event set into motion a series of events that would ultimately lead to Joseph rising to a position of power in Egypt and the eventual migration of his family there.