$ sudo apt-get update
$ sudo apt-get install freemind-plugins-help 

freemind-plugins-help is installed in your system.

Make ensure the freemind-plugins-help package were installed using the commands given below,

$ sudo dpkg-query -l | grep freemind-plugins-help *

You will get with freemind-plugins-help package name, version, architecture and description in a table

freemind-plugins-help package basic information: