Does Hell exist according to Catholicism? Does the Roman Catholic Church believe in the existence of Hell?

If YES - 


Who will go to Hell and why?
How long will they stay in Hell?
Is there any second chance after they go to Hell?
What should we do to avoid going to Hell?
The Catechism answers the questions (as ever!):


  1035 The teaching of the Church affirms the existence of hell and its eternity. Immediately after death the souls of those who die in a state of mortal sin descend into hell, where they suffer the punishments of hell, “eternal fire.”615 The chief punishment of hell is eternal separation from God, in whom alone man can possess the life and happiness for which he was created and for which he longs.



Those who die in a state of mortal sin will go to hell, because of that state.
They will stay in hell for eternity.
There is no second chance: it’s for eternity.
To avoid hell, they should ensure that they do not die in a state of mortal sin.


The difference between mortal and venial sins is also described in the Catechism. The best of way of not dying in sin is not to commit any; but since that is impossible, the Church provides the sacrament of Reconciliation [Confession] so that a penitent soul may be reconciled to God and man. This is the “second chance” which mankind feels is inherently “fair”: you get the second chance before death, while you can do something about your earthly, sacramental, life. Once that life is over you are out of reach of the sacraments.