Go to File -> Product Info -> About NVivo in the application
 to confirm which version of NVivo you are using.
For NVivo 12 and 11, go to File -> Help -> About NVivo

Help for NVivo Windows NVivo Help is quick and searchable Click Here
Help for NVivo Mac NVivo Help is quick and searchable Click Here
For previous versions of NVivo, please visit the Help sites below. 
Help for NVivo 12 Windows NVivo Help is quick and searchable Click Here
Help for NVivo 12 Mac NVivo Help is quick and searchable Click Here
Help for NVivo 11 Windows NVivo Help is quick and searchable Click Here
Help for NVivo 11 Mac NVivo Help is quick and searchable Click Here