Learning Buddha dharma we need to dive in to the dharma world. Without knowing the truth about Dharma we can not reach our enlightenment.
It's hard to know what Nibbana is without experiencing it. The same as it can't be known what an orange tastes like until it's taste is experienced, it can only be described with words. It's easier to say what it's not.
Nibbana is not nothingness or annihilation. Nibbana is the highest goal, better than the bliss of Heaven.
Nibbana is a state of great renunciation. There is Heaven within Samsara but it's imperminent and Nibbana is the final permanent liberation beyond Heaven and outside of Samsara.
Nibbana is an end of the cravings which cause all the suffering of birth, old age, disease, death, lamentation and fear.
Nirvana is the cure for our suffering here in the material world of Samsara caused by craving sensual pleasure and seeing reality as we want to see it rather than how it really is.
It's the correct understandung, virtue, peace and clarity of reality as it really is that leads to Nibbana.
Acoording to the Theravada tradition (or more precisely, the Mahasi tradition), Nibbana is state which is achieved towards the end of the insight cycle (magga-nana and phala-nana, fruition, called also "touch of Nibbana"); it is a state of extinction of consciousness, so there is nothing which can be said about it, there is no experience at all, and only when consciousness reappears, there is the knowledge that something has happened. It is said to have profound effect on the mind in destroying defilements. The state is termed supramundane, since there is nothing "mundane" (no time, no space, no consciousness).
Kenneth Folk talks about this in his excellent inverview at https://batgap.com/kenneth-folk/ .