Export your model as *.nif with the following settings.Select a bunch of polygons, elements, etc and assign them to ids and their bodyparts
(see appendix A1 for some examples) just make sure that important joints like knees, fingers, elbows, feet, shoulders, etc are where they belong or you will have to deal with heavy transformations during animations that do not look real in-game. Vanilla original, unmodified game assets How-To
Terms you should understand Skinning binding of a model to a rig/skeleton so that it moves according to the bones movement Uvw mapping unfolding of the mesh on a 2D plane so that you can paint it Texturing the painting of a model Normal mapping the creation of a secondary texture which determines light reflections and not modelled details like tiny groves, scars, etc.
