There are a few ways to block a website. One way is to use a web filtering tool like Net Nanny or similar software that prevent access to certain sites. These tools can be installed on your computer and will block websites based on category (e.g. adult, gambling, violence, etc.).
Another way to block a website is to add it to your hosts file. The hosts file is a list of IP addresses and domain names that your computer uses to resolve website addresses. By adding a website to your hosts file, you are essentially telling your computer that the site does not exist and it will not be able to load it.
Finally, you can also use a DNS blocking service like OpenDNS. This service will block websites at the DNS level, meaning that even if you type in the address of a blocked site, your computer will not be able to resolve it and the page will not load.