First thing you need is a 3D program that will do animations.
Then learn how to rig a model and create the motions.
Blender is free as is Art of Illusion.
I can't help you with those but study and play with them and you'll learn.
Being 14? You have lots of time.
There is no released Tool to change SH4 animations to SH3 animations.
Same with SH5 animations. No Tool released. Yet.
Now. S3D will export the animations of Secondary charaters. When you export the 3D model there is an extra tab to do so.
You'll get multiple obj files.