is there a special library or a course for learning fashion design on Autocad ?
AFAIK - No .
Autocad is not meant to be used for fashion ( technical term - Apparel ) design.
There are specific cad applications for that , that would let you create the seams , tensions , stitches and patterns .
Some of them are specifically used for presentation, others for production.
I have been using in the past clo3d ( http://www.clo3d.com/ ) , which is great for renderings (and begginers ) , less for production.
3Dsmax has special apparel tools ( the Cloth modifier and tools )
optitex is also quite good ( http://www.optitex.com/en/industries/fashion )
I suggest you use Google to find the tools . Just use the term "apparel CAD" and not "fashion" . You will find lots of forums, software ( some even free ) and tutorials.