ACCESS LIST

I have a cisco 3600 series router. since i do not have a application firewall i could not block some of the unwanted sites that i want to block. Is this possible to use the access list to block a particular sites using the ip address. For Eg. if i want to block one particular site’s ip address from being accessed by the users what is the exact command syntax and in the ip access-group command what is the spec i have to give is it in or out. Can any one help me out because when i tried this option the entire office is disconnected from the internet.

Thanks a bunch