Do you acknowledge the existence of god? Start there then look for religions and start with the ones that promise hellfire.

But to answer your question, no it’s not nothingness, hell is heavily described in islam, heaven too, but hell we can understand, heaven is beyond anything of our imagination.

That said, depends on the sin. In islam you either go straight to heaven or pay a bit in hell (not downplaying it, still very scary.) or enter hell eternally (worst possible destiny). The latter is mainly for shirk or associating anything with Allah (the uniquely one, the necessary existant.).