Adam and Eve really sold themselves to Satan—the evil, the devil—by doing as he wanted them to do. They traded their happiness for the knowledge of wrong which he promised them, and which he gave them.
Thus he became their owner, or master, instead of God who had made them, and to whom they really belonged.
Now they could not get free, and as the wages, or end of sin, is death, they must serve Satan all their lives and then die, without any hope of another life beyond this one.
God and Christ and the angels all pitied man in this sad condition, and Christ offered to leave Heaven and come to this earth and give His life for man's life.
Only in this way could He buy back, or redeem man (meaning everybody), so that all who want to be free from the service of Satan and sin can escape death, which is "the wages of sin."
Sometimes a rich man buys a slave from his cruel master, so that the poor man can be free and happy. So Jesus did for us.
We get free from Satan by thanking God for this plan to save us, and asking Him, for Christ's sake, to forgive our sins and help us to live a good life, away from our old master, the evil.
This is what the word Redemption means. It is buying back something that has been sold into bondage. Jesus bought us back after we had sold ourselves to Satan.
"Ye are not your own, for ye are bought with a price," "the precious blood [the life] of Christ." 1 Corinthians 6:19, 20; 1 Peter 1:18, 19.