What is nirvana and who believes in it?

Answer 1

Nirvana is the goal of Buddhism. All teachings of Buddhism are meant to the attainment of Nirvana. It is a state of mind, an understanding. It is essentially a realisation of the true nature of things in the world.

We are all in an illusion, not seeing this true nature of things, so we attach to things or dislike things. We crave for some things, want to own things. If we dislike something, we hate those. And sometimes there is confusion. (Craving, Hatred and Delusion)

Nirvana is when there is no attachments neither dislikes and no confusion. This is achieved through the eightfold path. Simply put by practicing to letting go, one can overcome Craving. By practicing loving kindness, one can overcome Hatred. And by meditation one can overcome delusion. These are further explained int the Eightfold path.