This is very soon going to get the prize for the most asked question
and most easily searchable answer. I'm getting really sick of people
who are too lazy to search for themselves and so waste the time of
others. It's very selfish.
However - from a Google FAQ that is VERY easy to find if you take the
trouble:
"Q: I have [thousands/several/at least two] links to my site, but when
I search on Google it says I have [zero/not that many] links. What
gives?
A: If you do a Google search using the link: operator (e.g.
[link:
www.example.com]), you will see a sampling of pages that link to
your site. For a more complete list of pages that link to you, verify
your site in Webmaster Tools and then click the Links tab to see the
sites that link to you."