God curses Satan for tempting and misleading Adam & Eve, This curse is to the Snake.
Genesis 3:15
And I will put enmity <0342> between thee and the woman, and between thy seed <02233> and her seed <02233>; it shall bruise <07779> thy head <07218>, and thou shalt bruise <07779> his heel <06119> .
0342 hbya 'eybah ay-baw' enmity, hatred
02233 erz zera` zeh'-rah seed, sowing, offspring, semen, descendants, posterity, children
07779 Pwv shuwph shoof bruise, break, cover, crush, gape upon, to fall upon
07218 var ro'sh roshe head, chief, top, beginning, company, captain, sum, first, principal, rulers
06119 bqe `aqeb aw-kabe' heel, footsteps, horsehoofs, footprint, hinder part, rear of a troop
So what this basically says is, the womans seed and offspring, will wound the head of the snakes offspring (or rulers), with the woman's offsprings heel or foot. If you believe or interpret the it as it is written, the Serpent Seed doctrine as it's most commonly known. Theres way more to this than I can explain here!
It's used 9 times in the Bible 1 more time in Isaiah, 2 times in Jeremiah, once in Daniel and Nahum, in addition to these verses and Genesis 3:15.
Isaiah 53:5
But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed. {wounded: or, tormented} {stripes: Heb. bruise}
Isaiah 53:10
Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand. {thou...: or, his soul shall make an offering}
Romans 16:20
And the God of peace shall bruise Satan under your feet shortly. The grace of our Lord Jesus Christ be with you. Amen. {bruise: or, tread}
EW Bullinger who was the only Christian scholar to edit the Massoretic Bible, states in his Commentary on this verse in Genesis says:
Gen 3:15 And I wil put enmity [hatred] between thee and the woman, and between thy [Satan’s] seed and her Seed; Christ shall bruise thy head [vital part], and thou shalt bruise His heel [lower part].
Refering to It or Christ in the 2nd part of this verse, Bullinger states: The corruption of this lies in the Vulgate. The verb tenses in the singular masculant shows that zer’a (seed) is to be taken in the singular tense. Hence the Septuigent form - i.e. of Christ; in Gen 17:7 you have the plural form of this word.
16 ... in sorrow [painful toil] thou shalt bring forth children ... 1Tim.2:14,15.
Childbearing was not brought forth into this world for eating an apple.
To see more on the serpent read Bullinger's Appendix 15 to the companion Bible!