12 occurrences Gehenna are mentioned in the New Testament, eleven of them used by Jesus for the ultimate destiny of the unsaved.

If you are unsaved, temporarily you will be held in hades before being sent to hell.

Gehenna was a word constructed from the valley of Hinnom where child sacrifices use to take place by nations to the bronze god of Molech by throwing their children into his fiery mouth. That began long before Israel got there. It became a garbage dumb for Israel and it was always burning.

Hell is the place reserved for Satan, the fall angels and demonic spirits. Jesus said in Matt. 25, "Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels" (v.41). In addition to fallen spirit beings, there are those on His left who take the mark of the beast or reject God's provision for eternal life through Christ. "And these shall go away into everlasting punishment: but the righteous into life eternal" "(v.46).

"And death and hades (or sheol) were cast into the lake of fire (Gehenna or Hell). This is the second death" (Rev. 20.14).

Even hades (sheol) will be concluded one day.