Facebook Ads Demographic / Behavior Filtering

Hello,

I have some specific questions while I'm setting up my ad targeting.

Under More Demographics | Work | Industries, I get the list of options like this:
- Industries
-- Administrative
-- Architecture and Engineering
-- Arts, entertainment, sports and media
-- Business and financial operations
-- Cleaning and maintenance
-- Community and social services
-- Computer and mathematics
-- Construction and extraction
-- Education and library
-- Farming, fishing and forestry
-- Food preparation and services
-- Healthcare and medical
-- IT and technical
-- Installation and repair
-- Legal
-- Management
-- Military
-- Personal Care
-- Production
-- Protective Service
-- Retail
-- Sales
-- Science
-- Temporary and seasonal
-- Transportation and Moving
-- Veterans (US)

I want to understand how this information is compiled for my target audience. For example,
1) Is this something users specified in their profiles?
2) If so, which field(s) in their profiles this data is coming from?
3) What specifically is categorized in "Computer and mathematics" and how is it different from "IT and technical"?
4) Where can I find a list of job titles that are categorized in each of the category?
5) If I have a specific target like "Bloggers" what will be the best demographic options to use?
6) Also, is there a page where I can find the exact details of each demographic option and behavior targeting? Instead of "You can use these demographic targeting options to select audience segments related to categories such as relationships, education, finances, and life events." which I can only find on Facebook help pages and it doesn't help me.

We have been using Facebook ads for a while and we want to understand in details so that we can expand our campaigns. Please kindly response.

Thanks!