If a section has enough activity where it is no longer capable of being managed by a Global Moderator, then a minion will be assigned. However, if you're active in an otherwise dead section, make releases for it and what not and actually get it active that's a good way to earn oneself a spot for the section. Once it's deemed necessary for a section to get a minion, the section may be offered to staff members who are already minion for other sections. If no one takes it, applications will be opened.
Hope that clears things up.