Read Job chapters 1 and 2.
Major Questions:
-> Who is this Satan character? What is its relationship to God?
-> Why are bad things allowed to happen to good people?
Part I: Who is the Satan?
Rabbi Yoḥanan says: Were it not explicitly written in the verse, it would be impossible to say this! The verse states: “You moved Me against him,” like a person whom others persuade and allows himself to be persuaded, as if God had not wanted to do anything, but allowed God's self to be persuaded to bring harm to Job.
Reish Lakish says: Satan, the evil inclination, and the Angel of Death are one... He is the Satan who seduces people and then accuses them, as it is written: “So the Satan went forth from the presence of the Lord, and smote Job with vile sores” (Job 2:7). He is also the evil inclination, as it is written there: “The impulse of the thoughts of his heart was only evil continuously” (Genesis 6:5) ...He is also the Angel of Death, as it is written: “Only spare his life” (Job 2:6); apparently Job’s life depends upon him...
The Sage Peleimu had the habit to say every day: "An arrow in the eye of Satan", mocking the temptations of the evil inclination. One day, it was the eve of Yom Kippur, and Satan appeared to him as a pauper who came and called him to the door, requesting alms. Peleimu brought out bread to him. Satan said to him: On a day like today, everyone is inside eating, and shall I stand outside and eat? Peleimu brought him inside and gave him bread. He said to him: On a day like today, everyone is sitting at the table, and shall I sit by myself? They brought him and sat him at the table. He was sitting and had covered himself with boils and pus, and he was doing repulsive things at the table. Peleimu said to the pauper: Sit properly and do not act in a revolting manner. Satan then said to him: Give me a cup. They gave him a cup. He coughed up his phlegm and spat it into the cup. They berated him for acting this way, at which point Satan pretended to sink down and die. They heard people around them saying: Peleimu killed a man! Peleimu killed a man! Peleimu fled and hid himself in the bathroom. Satan followed him and fell before him. Upon seeing that Peleimu was suffering, he revealed himself to him. Satan said to him: What is the reason that you spoke this way, provoking me by saying: An arrow in the eye of Satan? He replied: But what then should I say? Satan said to him: Let the Master, i.e., Peleimu, say: Let the Merciful One rebuke the Satan.
(7) I form light and create darkness, I make shalom and create evil— I the LORD do all these things.
בָּרוּךְ אַתָּה ה', אֱלהֵינוּ מֶלֶךְ הָעולָם, יוצֵר אור וּבורֵא חשֶׁךְ. עשה שָׁלום וּבורֵא אֶת הַכּל.
Blessed are You, Lord our God, King of the universe, who forms light and creates darkness, who makes and creates all things.
Part II: Why do bad things happen to Job?
It is all one; therefore I say, “He destroys the blameless and the guilty.”
...וְאִיּ֣וֹב עַבְדִּ֔י יִתְפַּלֵּ֖ל עֲלֵיכֶ֑ם כִּ֧י אִם־פָּנָ֣יו אֶשָּׂ֗א לְבִלְתִּ֞י עֲשׂ֤וֹת עִמָּכֶם֙ נְבָלָ֔ה כִּ֠י לֹ֣א דִבַּרְתֶּ֥ם אֵלַ֛י נְכוֹנָ֖ה כְּעַבְדִּ֥י אִיּֽוֹב׃
[God:]...And let Job, My servant, pray for you; for to him I will show favor and not treat you vilely, since you have not spoken the truth about Me as did My servant Job.
מיתיבי חסיד היה באומות העולם ואיוב שמו ולא בא לעולם אלא כדי לקבל שכרו הביא הקב"ה עליו יסורין התחיל מחרף ומגדף כפל לו הקב"ה שכרו בעוה"ז [כדי] לטרדו מן העולם הבא
There was a certain pious man among the nations of the world and his name was Job, and he came into the world only to receive his reward. The Holy One, Blessed be He, brought afflictions upon him, and he began to blaspheme and curse. The Holy One, Blessed be He, doubled his reward in this world in order to expel him from the World-to-Come...