NeverBlender is a plugin for the open source Blender 3D modelling, animation, and texturing application. It is the only currently-updated 3D modelling plugin (as of 2022), and as such, is probably used by more of the community than NWMax (a legacy set of plugins for GMax, itself a piece of legacy software that has not been supported for many years).
For those unfamiliar with either the Blender or GMax applications, you are likely to be better off starting with Blender given that it has more up-to-date documentation available online and is a modern piece of software. However, it is worth noting that some major custom content creators in the community still use NWMax, and some GMax tools can still produce better results than their modern Blender counterparts (for example, the GMax 'optimize' tool is significantly better at reducing the polys in a mesh whilst keeping it intact, versus Blender's 'decimate' modifier).
The three tutorials linked below (i) introduce you to the basics of Blender, (ii) walk you through the basics of exporting a placeable in NeverBlender, and (iii) introduce you to the proper NWN scene set up in NeverBlender of parent nodes and sub-objects, so that you can export models which will work properly in-game.
NeverBlender install instructions can be found here
(Note that as of May 2023, NeverBlender is only supported by Blender versions up to v3.3; Blender 3.4 is not supported. Check the vault page (link above) for full list of compatible versions).
NeverBlender 101: Part 1 - Introduction
This tutorial will show you the basics of Blenders user interface.
NeverBlender 101: Part 2 - Creating a simple Placeable
This tutorial will show you how to export an simple placeable. There will be no modeling involved, this is only about the general process and structure of the scene.
This tutorial will show you how to set up scenes and objects in order for NeverBlender to correctly export the model.