Questions about Autoplay on Windows 7?

I leant my laptop to my cousin because i was having problems getting certain programs to work. He is a computer technician and when he gave it back all the problems were resolved however he told my that he turned off autoplay as it is considered by some to be a security risk and said that it can be reactivated through the control panel.

Here are the questions i have:

1. What is autoplay, what does it do, and is it safe?

2. Will turning autoplay off affect the ability of installed programs to update themselves? The main one i am concerned about is HP Support Assistant as it updated itself around this time last year.

3. If i have to turn it back on what is the easiest way to do so? I am assuming i can do so through the control panel like he said, is this correct?

Please explain in laymen's terms as i no next to nothing about computers.