What browser do are you using? Safari and Firefox requre different methods.
With Safari, go to Safari/Preferences/Privacy and select Remove All Website Data. On the same page, you can choose to block your computer from keeping cookies in the future.
With Firefox, go to Firefox/Preferences/Privacy and make a selection in the same manner. You have a similar option to block future cookies.
I presume you know all the arguments about cookies. They do serve a legitimate function, and allow you to customize your MBP relative to your interests. If you value privacy, you might want to purchase an excellent application, 1Password http://agilebits.com/products/1Password/Mac , which allows individual selection of all sites that you might use. If you require a password, like for this forum, the information is added instantly and securely. It's $39.99, and offers a free trial.
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