1. Browse to C:\Windows\System32\drivers\etc.
2. Look for a file named as hosts, then open it with Notepad.
3. At the bottom of the file, add the line as shown below:
127.0.0.1 www.facebook.com
www.facebook.com is an example of website URL which you would like to block, just replace it with the actual URL so that they are unaccessible to all.
4. If you have more websites that would like to be blocked, just press Enter and repeat step 3 to add additional URL until all desired websites are added.
5. At the last line of the URL that you have entered, add an extra carriage return by pressing Enter.
6. Save and close the file.