Toldot means “offspring” and “generations”; it also means “generations” in the more general sense—that which a person generates and produces. Thus, “the toldot of Isaac” are Isaac’s two sons, Jacob and Esau, as well as the deeds and achievements of Isaac—both of which are the subject of the Torah section of Toldot.
These are the generations of Isaac the son of Abraham—Abraham fathered Isaac.
Isaac was forty years old when he took Rebecca the daughter of Bethuel the Aramean of Padan Aram, the sister of Laban the Aramean, to himself for a wife.
But twenty years later, the couple was still childless.
Isaac prayed to G‑d opposite his wife, because she was barren, and G‑d accepted his prayer, and Rebecca his wife conceived.
Rebecca had a tumultuous pregnancy, as “the children struggled within her.” When she inquired to G‑d as to the meaning of this, she was told:
Two nations are in your womb, and two peoples shall diverge from your belly. One nation will struggle against the other; and the elder shall serve the younger.