Everything that will occur is already decreed by Allah

Mankind has a real will and choice

Human will operates under Allah’s will

People are accountable because they choose their actions
This is the balanced belief between the extremes of al-Jabriyyah and al-Qadariyyah.

Allah Created and Decreed All Things
Allah says:
إِنَّا كُلَّ شَيْءٍ خَلَقْنَاهُ بِقَدَرٍ
Translation:
"Indeed, We have created everything with Qadr."
Reference: Qur'an: 54:49

All Deeds Are Written Before Creation
The Prophet ﷺ said:
إِنَّ اللَّهَ كَتَبَ مَقَادِيرَ الْخَلَائِقِ قَبْلَ أَنْ يَخْلُقَ السَّمَاوَاتِ وَالْأَرْضَ بِخَمْسِينَ أَلْفَ سَنَةٍ
Translation:
"Allah wrote the decrees of creation fifty thousand years before He created the heavens and the earth."
Reference: Sahih Muslim: 2653

Paradise and Hell Are Already Known to Allah
The Prophet ﷺ said:
إِنَّ أَحَدَكُمْ يُجْمَعُ خَلْقُهُ... فَيُكْتَبُ رِزْقُهُ وَأَجَلُهُ وَعَمَلُهُ وَشَقِيٌّ أَوْ سَعِيدٌ
Translation:
"His provision, lifespan, deeds, and whether he will be miserable or happy are written."
Reference: Sahih al-Bukhari: 3208
Reference: Sahih Muslim: 2643
Second: Humans Have a Real Will and Choice

Allah Affirmed Human Choice
Allah says:
فَمَنْ شَاءَ فَلْيُؤْمِنْ وَمَنْ شَاءَ فَلْيَكْفُرْ
Translation:
"So whoever wills let him believe, and whoever wills let him disbelieve."
Reference: Qur'an: 18:29

Humans Are Accountable for Their Actions
Allah says:
كُلُّ نَفْسٍ بِمَا كَسَبَتْ رَهِينَةٌ
Translation:
"Every soul is held in pledge for what it has earned."
Reference: Qur'an: 74:38
If humans had no will, accountability would be meaningless.
Third: Human Will Is Under Allah’s Will

The Correct Balance
Allah says:
وَمَا تَشَاءُونَ إِلَّا أَنْ يَشَاءَ اللَّهُ رَبُّ الْعَالَمِينَ
Translation:
"And you do not will unless Allah wills, Lord of the worlds."
Reference: Qur'an: 81:29

Humans will and choose

Allah allows and creates that choice