فَإِنَّ اللَّهَ تَعَالَى خَلَقَ الْجَنَّةَ وَالنَّارَ قَبْلَ الْخَلْقِ وَخَلَقَ لَهُمَا أَهْلًا
Allah Most High created Paradise and Hell before creating His creatures, and He created inhabitants for both.
The two abodes are already created, and the people destined for them are within Allah's knowledge and decree. These are related aspects of belief about the Hereafter.