Hell is the eternal damnation of those, who due to their free choice, die in mortal sin without repenting for it and without accepting the merciful love of God. Jesus expresses such a reality with some images: Gehenna, inextinguishable fire, burning furnace… They are images to describe the state of extreme suffering and of eternal damnation which affect those who are in hell;
The main punishment of hell consists of eternal separation from God: only in Him in fact man can have life and happiness, for which he has been created and to which he aspires.
God does not predestine anyone to go to hell. Rather He, as a good Father, desires that everyone be saved and reach His Home: Paradise. He therefore sent His Son who died and was raised. He does not want “that anyone should perish, but that all should come to repentance” (2 Pt 3: 9). He thus wants that every single person during his earthly life either kindly (benevolently) or sometimes even in a strong manner (as every good father does with his own son). And nevertheless, having created man free, God respects the decisions of every person, especially in the crucial moment of his death. Therefore it is man himself who, in full freedom and responsibility, excludes himself from Paradise and, by persisting in his radical refusal of God, merits hell.