On the internet the Domain Name System (DNS) translates web site names like www.facebook.com to a string of numbers that is the website's location on the Internet. For example, without DNS translating computer names to IP addresses you would have to type http://184.108.40.206/ in your web browser to get to Facebook instead of www.facebook.com.
Normally you get DNS name translation from your Internet service provider, but DNS is a standardized service and you can use anyone's DNS services to provide DNS name translations.
There are several companies on the web that offer free DNS services for users which keep track of bad guy sites and intentionally do not translate bad guy web site DNS names to IP addresses. If you use their services you have what is essentially a firewall preventing you from accessing the bad guy sites. Both Google and a company called OpenDNS offer these services.
In order to keep this article short I'll just say that I would recommand you try out OpenDNS's Familyshield DNS services. They have straightforward instructions on how to set yourself up to use their DNS service.
Here's the link: