Calibre tags

hi,

I installed Calibre portable on a thumb drive.
I would like to use tags to group my books.

Out of the box there are no tags which is understandable.

How do I setup my list of tags so I can use the dropdown tag box under edit meta data.:help:

Can you nest tags like say

Math
__general
____matrices
____Taylor series
____Bessel function
____DE


any help would be much appreciated.
pzaw