'Nor' is a conjunction that is used in negative constructions.
It is typically used as a correlative conjunction to introduce the second or subsequent element in a negating expression. For example, it is used with 'neither' to express a double negative. It can also be used to express contrasting ideas ('He is not tall, nor is he short') or serve as an adversative conjunction introducing contrasting phrases or clauses ('Neither was she happy, nor did she understand the situation').
1. 'I neither study nor did I pay attention in class.'
2. 'He has neither the desire nor the capacity to do this job.'
3. 'She is neither tall nor short.'
While 'nor' can be used to express contrasting ideas (example 2), it is not usually used after 'not' for this purpose (it is more common to use 'but' instead, as in 'She is not tall, but short'). Additionally, 'not... nor' is typically preceded by an auxiliary verb (example 1), although this isn't always the case (example 3).