Newbie Question

I decided to try the service to scan my computer/ip and since I have no idea what some of the results meant…

Plugins Available: 21433
Plugins Used: 21433

Time started : 2008-05-05 17:28:15
Time finished : 2008-05-05 17:28:34
Audit time : 0:19

No vulnerabilities were found and the host did not respond to any of our checks, this may be because:

* The host is currently unreachable.
* No services are available on the host and it is secure.

What does the plugins mean?

I get the “No vulnerabilities” part but is it that quick? 19 seconds?

So is my comp safe? ><