I would copy paste this, but due to the nature of the forum that would mean a lot of formatting work. So I'm just going to post a link and leave it to a TR member to convert it if they deem it worth the while.

https://forum.openmw.org/viewtopic.php?f=33&t=3330

This includes instructions on how to install OSG plugin, how to export osgt files, how to make OSG collision boxes, OSG animations, how to install blender nif plugin, how to export nif files, how to make nif collision boxes, how to work with animation groups in nif files, etc. It will be updated as new things arrive and we figure stuff out over at the OpenMW forums.