Follow this steps:
- Click on your profile name on right-top side of screen.
- Choose "Theme Options".
- in theme's option page Turn ON "Enable Advanced Category" option and save the form.
please read the guidelines about this theme's features and capabilities:
Limitation & Features for using Advanced Category Field:
- only works with first level categories(No Sub-Categories)
- User must be able to select no categories
- User will be able to create categories while asking questions
- Administrator will be able to add icons or detail to each category in "admin > categories" page