Isaac is forty when he gets hitched to Rebekah. He prays to the Lord for his barren wife to become pregnant, and, bam, Rebekah's barren womb is filled. Two babies, actually. That's some good praying.
The babies wrestle in her womb, and Rebekah goes somewhere to ask the deity what's going on.
The Lord tells her that one of them is stronger than the other, and the elder will serve the younger. That's the norm in Genesis (just think of Ishmael-Isaac), but backwards in terms of the larger social world, where the firstborn is usually top dog.
The first twin born is Esau, and he's red and hairy. Hmmm. These kinds of descriptions of the character's physical appearance are rare in biblical narratives. Why here?
The second twin grabs the heel (Hebrew: 'aqeb) of the first, so he is called Jacob (Hebrew: ya'aqob).
Jacob is "plain" (25:27 KJV) or "quiet" (NRSV). The adjective can mean something like "morally astute," which is of course ironic given Jacob's subsequent actions.
Isaac loves Esau, who, as a skillful hunter, brings his dad lots of juicy meat. But Rebekah loves Jacob, who's a mama's boy and stays near the tents.
One day, Jacob cooks up some stew. Esau comes in from the field, starving, and asks somewhat brutishly for some "red stuff" (25:30 NRSV).
And that, folks, is how Esau gets his nickname, Edom, which plays on the Hebrew for "red stuff" ('adom). Edom will be one of Israel's future enemies.
Jacob negotiates: some stew for Esau's birthright.
Sounds sketchy to us, but Esau's starving to death, so it seems like a good deal to him.
Esau swears his birthright over to Jacob, and in return, Jacob gives him the stew, plus some bread. The bread is free. No charge.
Esau eats, drinks, rises, and goes off. The narrator remarks that he clearly doesn't value the birthright.