[Plugin: BP Group Categories/Types] Creating sub-categories

I’m having a little trouble figuring out how to create sub-categories.

(1) Once I create main category 1 and assign ID 1, how do I create sub-category to appear under main category?

(2) I would like to create several categories and sub-categories myself and for each new member, they would have to fill in a required field that would automatically assign them to that main category. The member then would have the option to select the sub-category already available or create another one under the same main category.

Is that would this plugin will end up helping us to do? If not, please just help me with item (1). Thank you in advance 🙂

http://wordpress.org/extend/plugins/bp-group-categoriestypes/