To be more productive some time you may want to block some website. In my case sometimes I block amazon.com, amazon.in, facebook.com.
To block website you need to edit your host file
go to terminal and type
sudo vi /etc/hosts
It will ask for your password
in hosts file add the following line
127.0.0.1 www.facebook.com
127.0.0.1 www.amazon.com
you can add as many as you want to your host file. State above example block www.facebook.com and www.amazon.com.
You may find out some time those example not work with out reboot. In this case you need to clear dns cache
just type following line in terminal to clear cache
dscacheutil -flushcache