system
A chat on 4chan
human
As far as my understanding goes, the main premise of Buddhism (especially Theravadin) is that existence in an of itself is absolutely pointless. The cycle of rebirth (i. e. Samsara) has no begining, no end and no overarching meaning. To exist is to inevitably experience dukkha, which is the whole spectrum of unease from getting your limbs hacked of by a deranged cartel member, to the subtlest states of tension still present in deep meditative states. Desires and attachments create not only suffering in this life, but karma, which is essentially a mental force that leads to renewed birth. So, the aim of meditation is to attain a certain way of seeing all conditioned phenomena (i. e. whole Samsara) - that they are impermanent (anicca), inevitably lead to some sort of stress (dukkha) and are not-self (anatta; some say that this means that phenomena themselves have no intrinsic nature, but this in my eyes would be more in line with the idea of sunyata; not-self, in practical terms, means not worth identifying with). The question arises if these criteria are just heuristics used in order for letting-go to occur, or if they truly are ultimate truths.
gpt
Regardless of the above, upon letting go, the mind attains Nirvana. Whatever the fuck that means has been debated for the past 2,5 k years by now. Some say it means just that the cycle of rebirth is ended and the arahant, after physical death, just ceases to exist and that's that. I personally think that Ajahn Thanissaro's analysis in 'The mind like fire unbound' has a good basis. Basically, he notices that the Buddha in the suttas often invoked images of extinguishing fire when describing the attainment of Nirvana. He discovers that in those days in India, a flame was seen as an agitation of a latent, inactive fire element that was spread throught space. A flame in their eyes was that unagitated element that had become attached to fuel and agitated. So, assuming this premise is correct, it would mean that the extinguishment of fire (i. e. cessation of desires and attachments) symbolises not annihilation, but rather a return to an unagitated, unconditioned state. He also says that this can't be classified as eternalism, as Nirvana is an unconditioned principle that lies beyond Samsara and thus time - a part of conditioned reality - ceases to apply there.

All in all, I highly recommend reading the aformentioned book (at least the Abstract) if you want to gain a deeper understanding of Buddhism. And the confusion is understandable - it's hard not to get confused when trying to grasp a religion that's been fermenting for the past two and a half millennia, especially when one tries to get to the core.