I guess I need to give you a step by step guide.
Install Calibre and PyCrypto:
Download zip archive with plugins.
sudo apt-get install calibre python-crypto
You'll get three folders. The plugins for Calibre are in Calibre_Plugins. Notice where you are in the directory tree.
Read the ReadMe files there. They explain how to install the plugins in Calibre.
Open Preferences / Change calibre behavior (three gears icon) or press Ctrl+P
In the Advanced row select Plugins
Click on the button Load plugin from file in the bottom row.
Navigate to the folder Calibre_Plugins where you've unpacked plugins.
Select plugin you want to install and click on the Open button.
Confirm your choice.