Before you can install Softaculous, you need to enable ioncube loader for PHP. This can be done in WHM (root) > Server Configuration > Tweak Settings > PHP. Select ioncube check box for cPanel PHP loader and click save button. This will enable Ioncube for you in 3rd party PHP binary.

To install softaculous, run

wget -N http://files.softaculous.com/install.sh
chmod 755 install.sh
./install.sh

This will take some time as it need to download all software it auto installs.

If your server IP have license, it will be auto activated by default.