Download and install Visual Studio 2015 - Make sure to save the ISO as it's only available using unoffical methods.
https://go.microsoft.com/fwlink/?LinkId=615448&clcid=0x409
Download and install Office/Sharepoint Development Kit/Tools:
https://blog.devoworx.net/2016/07/14/office-sharepoint-template-missing-in-visual-studio-2015/
Create first Add-In!