I mentioned phishing recently. I just got a phishing attempt in one of my email accounts so I have a good example to show.
The following email looks like it might be from eBay, but it is from an Internet criminal. The links in phishing emails usually lead to fake web sites where you are tricked into giving your credit card or other financial information. Notice how the email describes how you will need to update your credit card information.
Because this email is addressed to "eBay user" and not my real name, I know it is probably fake. Another clue that it is fake is that I don't have an eBay account. If I couldn't determine whether it were real or not, I would open a browser and type in http://www.ebay.com and login on the actual eBay site. Never click on links in these kinds of emails.