Right and wrong before the Law

The law of Moses contains a list of the animals God considers clean and of those that are unclean. It appears in Leviticus 11.  Clean animals could be eaten and many of them were acceptable as sacrifices to God.  Unclean animals were not acceptable either as food or as sacrifices.  Noah lived long before God gave the law but he knew the difference between clean and unclean animals.  This is shown by the instructions God gave him as to what animals he should take on the ark.

Take with you seven pairs of all clean animals, the male and his mate, and a pair of the animals that are not clean, the male and his mate.
Genesis 7:2

The extra clean animals were intended to enable him to offer sacrifices to God.

Then Noah built an altar to the LORD and took some of every clean animal and some of every clean bird and offered burnt offerings on the altar.
Genesis 8:20

The law commanded the people to give a tenth of their income to God.

Every tithe of the land, whether of the seed of the land or of the fruit of the trees, is the LORD’s; it is holy to the LORD. If a man wishes to redeem some of his tithe, he shall add a fifth to it. And every tithe of herds and flocks, every tenth animal of all that pass under the herdsman’s staff, shall be holy to the LORD.
Leviticus 27:30-32

Abraham and Jacob practiced tithing before Moses commanded it.

And Melchizedek king of Salem brought out bread and wine. (He was priest of God Most High.) And he blessed him and said,
“Blessed be Abram by God Most High,
Possessor of heaven and earth;
and blessed be God Most High,
who has delivered your enemies into your hand!”
And Abram gave him a tenth of everything.
Genesis 14:18-20

Then Jacob made a vow, saying, “If God will be with me and will keep me in this way that I go, and will give me bread to eat and clothing to wear, so that I come again to my father’s house in peace, then the LORD shall be my God, and this stone, which I have set up for a pillar, shall be God’s house. And of all that you give me I will give a full tenth to you.”
Genesis 28:20-22

The law mandated a practice called levirate marriage, the requirement that if a man died without children his brother must marry his widow in order to produce children to carry on his line.

If brothers dwell together, and one of them dies and has no son, the wife of the dead man shall not be married outside the family to a stranger. Her husband’s brother shall go in to her and take her as his wife and perform the duty of a husband’s brother to her. And the first son whom she bears shall succeed to the name of his dead brother, that his name may not be blotted out of Israel.
Deuteronomy 25:5-6

Judah was familiar with this practice before this law was given.  When his oldest son died he ordered his second son to marry the first son’s widow.

And Judah took a wife for Er his firstborn, and her name was Tamar. But Er, Judah’s firstborn, was wicked in the sight of the LORD, and the LORD put him to death. Then Judah said to Onan, “Go in to your brother’s wife and perform the duty of a brother-in-law to her, and raise up offspring for your brother.”

But Onan knew that the offspring would not be his. So whenever he went in to his brother’s wife he would waste the semen on the ground, so as not to give offspring to his brother. And what he did was wicked in the sight of the LORD, and he put him to death also.

Then Judah said to Tamar his daughter-in-law, “Remain a widow in your father’s house, till Shelah my son grows up”—for he feared that he would die, like his brothers. So Tamar went and remained in her father’s house.
Genesis 38:6-11

One of the ten commandments prohibited adultery.

You shall not commit adultery.
Exodus 20:14

Joseph knew adultery was a sin even though he never heard this commandment.

After a time his master’s wife cast her eyes on Joseph and said, “Lie with me.”

But he refused and said to his master’s wife, “Behold, because of me my master has no concern about anything in the house, and he has put everything that he has in my charge. He is not greater in this house than I am, nor has he kept back anything from me except you, because you are his wife. How then can I do this great wickedness and sin against God?”

And as she spoke to Joseph day after day, he would not listen to her, to lie beside her or to be with her.
Genesis 39:7-10

Many think of the law of Moses as introducing completely new standards of right and wrong.  It did contain new elements, such as the Levitical priesthood, tabernacle worship, and the introduction of the Passover and other annual holidays, but a large part of it consisted of putting into writing the standards of conduct that the people were already practicing.