'Browse file' is what you get if you click 'load' (file). With this, you can open an existing .ztd file in Ape.
About 3D animals.. you need a 3D program to get started. Blender or anim8tor are free ones. (Google can find you them fairly easy.) It isn't very easy though, to make. And I can't explain it in one post.. It's best that you look up the tutorials available on the web.
As for ZT2, you can't import your 3D animals in them, because the format they have to be saved in (format = (f.e.) .jpeg, .bmp) is protected. No fans know how to convert your 3D model into .nif (=format of ZT2).