What's difference between "Person" "Organization" and "Direct" into Request Non Catalog Learning?

Hello everyone

I need to submit a Request Non Catalog Learning but first of all I need to know the difference between "Person" "Organization" and "Directs" al the level of Learners section. I've attached the screen for more clarify

I'd like to receive answer at the question below:

• If select "Person" which user can I select?
• If select "Organization" which user can I select?
• If I select "Direct" which user can I select?

Thank you

Fabio