Abel was the first son of Adam and Eve. Abel's older brother Cain was his half brother because Adam was not Cain's father.
Yahweh knew what happened, because Yahweh knows everything, and He asked Cain, Where is Abel? Cain was very rude to Yahweh and said, I don’t know, do I look like my brothers keeper? Yahweh didn’t like that.
Yahweh said to Cain, I know you killed Abel, and now, to pay for what you’ve done, whenever you plant something, it won’t grow. You will not have a home and you will run from place to place on the earth and hide your face from Me. Cain begged Yahweh, Please don’t punish me so hard, it’s more than I can take. Anyone that finds me will want to kill me.
So Yahweh put a mark on Cain to protect him from being killed. Adam and Eve had another son after that, and called his name Seth.
Abel's name in Hebrew is Hebel, meaning breath.
Now, since Cain brought only the fruit of the ground for his first offering to Yahweh, it shows that he did not have the spiritual insight of the pure Adamic seed which Abel had.
Abel brought the firstlings of his flock and the fat thereof. Abel sacrificed the first of the flock to Yahweh
The book of Jasher goes into much more detail.
7 And in some time after, Cain and Abel his half brother, went one day into the field to do their work; and they were both in the field, Cain tilling and ploughing his ground, and Abel feeding his flock; and the flock passed that part which Cain had ploughed in the ground, and it sorely grieved Cain on this account.
18 And Cain approached his brother Abel in anger, and he said unto him, What is there between me and you, that you comest to dwell and bring your flock to feed in my land?
19 And Abel answered his brother Cain and said unto him, What is there between me and you, that you shalt eat the flesh of my flock and clothe yourself with their wool?
20 And now therefore, put off the wool of my sheep with which you hast clothed yourself, and recompense me for their fruit and flesh which you hast eaten, and when you shalt have done this, I will then go from your land as you hast said.
21 And Cain said to his brother Abel, Surely if I slay you this day, who will require your blood from me?
22 And Abel answered Cain, saying, Surely God who has made us in the earth, He will avenge my cause, and He will require my blood from you shouldst you slay me, for Yahweh is the judge and arbiter, and it is He who will requite man according to his evil, and the wicked man according to the wickedness that he may do upon earth.
23 And now, if you shouldst slay me here, surely God knoweth your secret views, and will judge you for the evil which you didst declare to do unto me this day.
24 And when Cain heard the words which Abel his brother had spoken, behold the anger of Cain was kindled against his brother Abel for declaring this thing.
25 And Cain hastened and rose up, and took the iron part of his ploughing instrument, with which he suddenly smote his brother and he slew him, and Cain spilt the blood of his brother Abel upon the earth, and the blood of Abel streamed upon the earth before the flock.
Cain and his children are responsible for killing many righteous people from the old days until now.
Book of Adam and Eve 83:34 Cain said to Abel, "O brother, the country is so beautiful, and there are such beautiful and pleasurable trees in it, and charming to look at! But brother, you hast never been one day in the field to take your pleasure therein.
35 "To-day, O, my brother, I very much wish you wouldest
come with me into the field, to enjoy yourself and to bless our fields and our flocks, for you art righteous, and I love you much, O my brother! but you hast estranged yourself from me."
36 Then Abel consented to go with his half brother Cain into the field.
37 But before going out, Cain said to Abel, "Wait for me, until I fetch a staff, because of wild beasts."
38 Then Abel stood waiting in his innocence. But Cain, the forward, fetched a staff and went out.
39 And they began, Cain and his half brother Abel, to walk in the way; Cain talking to him, and comforting him, to make him forget everything.
84:1 AND so they went on, until they came to a lonely place, where there were no sheep; then Abel said to Cain, "Behold, my brother, we are weary of walking; for we see none of the trees, nor of the fruits, nor of the verdure, nor of the sheep, nor any one of the things of which you didst tell me. Where are those sheep of yours you didst tell me to bless?"
2 Then Cain said to him, "Come on, and presently you shalt see many beautiful things. but go before me, until I come up to you."
3 Then went Abel forward, but Cain remained behind him.
4 And Abel was walking in his innocence, without guile; not believing his brother would kill him.
5 Then Cain, when he came up to him, comforted him with his talk, walking a little behind him; then he hastened, and smote him with the staff, blow upon blow, until he was stunned,
6 But when Abel fell down upon the ground, seeing that his half brother meant to kill him, he said to Cain, "O, my brother, have pity on me. By the breasts we have sucked, smite me not! By the womb that bare us and that brought us into the world, smite me not unto death with that staff! If you wilt kill me, take one of these large stones, and kill me outright."
7 Then Cain, the hard-hearted, and cruel murderer, took a large stone, and smote his half brother with it upon the head, until his brains oozed out, and he weltered in his blood, before him.
8 And Cain repented not of what he had done.
9 But the earth, when the blood of righteous Abel fell upon it, trembled, as it drank his blood, and would have brought Cain to naught for it.
10 And the blood of Abel cried mysteriously to God, to avenge him of his murderer.
11 Then Cain began at once to dig the earth wherein to lay his half brother; for he was trembling from the fear that came upon him, when he saw the earth tremble on his account.
12 He then cast his half brother into the pit he made, and covered him with dust. But the earth would not receive him; but it threw him up at once.
13 Again did Cain dig the earth and hid his half brother in it; but again did the earth throw him up on itself; until three times did the earth thus throw up on itself the body of Abel.
14 The muddy earth threw him up the first time, because he was not the first creation; and it threw him up the second time and would not receive him, because he was righteous and good, and was killed without a cause; and the earth threw him up the third time and would not receive him, that there might remain before his half brother a witness against him.
15 And so did the earth mock Cain, until the Word of God, came to him concerning his half brother.
Abel still awaits wrath and vengeance to Cain and his seedline. Cain is cursed FROM the ground. It will never again yield it's bounty to his seedline. Cain is the first Jew. Jews are not farmers.
Abels' blood still cries out for vengeance from the ground. Abel will be avenged when our Prince Yahshua Christ returns.