In your office or home you have to block some websites. Using this steps, you can block any website without any softwares...
Find the file named as "hosts"
Open it in notepad
Under "127.0.0.1 localhost" Add 127.0.0.2 www.sitenameyouwantblock.com (without # symbol) , and that site will no longer be accessible.
File -> Save .
For every site after that you want to add, just add "1" to the last number in the internal ip (127.0.0.2) and then the addy like before.
-Now these sites are blocked from your computer.