When we die, we choose where our souls go.
If we choose to be with God, we go to him to be with him.
If we choose something other than God, that is where our souls spend eternity.
God does not want any soul to suffer, he calls all to Himself....but God respects the free will with which he has endowed all human souls.
The human soul was made to be in union with nothing less than the greatest and the best. It was made in the image of God.
However, some of us will love other things more than we love God.
There is nothing in existence that is intrinsically evil. God made all things, and they are all good.
However, evil consists of essentially assigning a higher value to something than it ought to have. It is a disordered love.
Some souls will love lesser things more than greater things, even the greatest thing of all, and they will choose the lesser at death for themselves.
To spend eternity with anything less than what our souls were made for is what I would call Hell.
Even in this life, we see people taste Heaven and Hell for themselves, but this is just a shadow of what these things really are.
The joy of heaven and the misery of hell are experienced fully after we die.