The new Google Mail has a great built in spam filter, but for it work effectively you will need to "train" it. Here's how:
Look at the bottom of the left menu in your email account. You'll see the word "More" and a drop-down arrow. Click the arrow.
Notice the "More" becomes "Less" and you can now see the Spam link. The number in parenthesis represents the number of messages in the spam folder. Click Spam.
You will be presented with a list of messages that Google has determined are spam. You may find a message or messages in this list that are legitimate.
When you place a checkmark beside an entry, two new buttons appear at the top of the list: Delete forever and Not spam. Once you have placed a checkmark beside the legitimate email(s), click the Not spam button. The checked email(s) will be moved from the spam folder to your inbox. You should check your spam filter regularly for a while because it may take several times before Google will "learn" that certain emails you receive are not spam.
You may find an email in your inbox that IS spam but Google did not move it to your Spam folder. What then? This one is also a simple fix.
Just put a checkmark beside the spam email and you will see three new buttons at the top of the list of emails: Archive, Report Spam, and Trash.
Check the Report Spam button and the email will be reported to Google for investigation and then be deleted from your inbox. Use this feature carefully. If you have legitimately subscribed to a newsletter that you no longer wish to receive, you should use the unsubscribe feature that is provided in the email. If you report a legitimate email as spam you are telling Google that the sender is a spammer and this could cause the sender to be blacklisted. Google takes this seriously, so please make sure that you are in fact reporting spam.