There are no significant changes to the custom solutions development process between Microsoft SharePoint Server 2013 and SharePoint Server 2016.
For more information about documentation, training, and technical articles for developing solutions and customizing SharePoint Server 2013 and 2016, see the following Microsoft resources:
.NET server API reference for SharePoint
.NET client API reference for SharePoint
SharePoint general development
Office Development - SharePoint 2013
For more information about documentation, training, and technical articles for developing solutions and customizing SharePoint Server 2013 and 2016, see the following Microsoft resources:
.NET server API reference for SharePoint
.NET client API reference for SharePoint
SharePoint general development
Office Development - SharePoint 2013