Nirvana is not a place but could be described as a state of mind - a mind that sees things as they really are and not clouded by delusion. Yet it is more than just a state of mind. It transcends speculation and description. God means different things to different people. Some will say that it refers to an anthropomorphic being like ourselves who created the world whilst others, such as the Christian Philosopher of Religion, Paul Tillich, suggests that God is the ground of being - the very fact of existence, whereas others prefer not to define God because such things as descriptions are inadequate when speaking of the transcendental.
All descriptions are inadequate.
The Fourth Noble Truth is the method taught by the Buddha for attaining this state of Nirvana. It is the Noble Eightfold Path. One who walks the Path is considered to be a noble or worthy person. Understanding is knowledge that the Four Noble Truths lead to the overcoming of Dukkha. It does not imply a total understanding of these Truths but a confidence that, by following the Path, the result, Nirvana, will be attained.