In Facebook, how to hide Friends lists but show my Friends to Friends only?

I saw on one of my friends profile, that his friends were grouped into categories like - some friends in "Work", some friends in "School", etc.
How to make such friend list groupings?

Also, please tell me how to make that groupings private. I mean, though my friends can see my friend list, but i do not want to show them in what group they have been put into (like work, school, college, etc.)