How to check the information is true or false?

[Clarence Huang]

Many people tell me, "You should check the answer on the Google
Search Engine before you ask a question" ,  but  How  do I know that
information is true or false?

When I first time ask a question on Debian IRC Channel, they usually
tell me this sentence, and now the mailing list guide tell every want
to ask a question on the mailing list  try to google your answer, but
how should we  know the asnwer is true or false?