Sand box Knowledge

Hi
I want to know that how i come to know about the sand box? what is it? why sites going to sand box? and how i will get the idea that my site is in sand box or not?

first of all i only got your last question
for that just type in google
site:yoursitename.com
if u see any results than u arnt sandboxed
if you see NOTHING NO results
than u are sandboxed
u usualy get sandboxed for spaming your site without control.. ie bad seo