To manage Parental Controls, open the Windows Control Panel, click "Set up
parental controls...", and consent to the security elevation box.
Select the user account that you want to manage. (If you don't have a
separate user account for each person who will regularly use the computer,
you should consider making one, as everything tends to work better that way).
Windows will let you turn Parental Controls on, and then manage more
detailed settings (for example, enforcing usage time limits or blocking
certain programs).
To test the parental controls, try blocking all games on your child's
account. Log out of your account, and log in under your child's account.
Try running "Solitaire" while logged in under your child's account.
If you get an error message while doing any of the steps above, post it
here, and we'll see if we can help you.
As an aside, actually trying to block every "bad" website is almost
impossible. The internet has many, many "bad" websites, and clever people
can find more than one way to access a website (for example, Firefox does not
currently obey any restrictions).