I would say the ugly pigtail thing attaches to the output side of the charge controller. We really don't know what the panel's junction box looks like, what wires it has, etc. It "probably" has the standard black weather-resistant j-box on it, and may or may not have MC4 wires attached. If not, simply buy an MC4 6 foot "extension cable". Cut it in half and connect it to the j-box. Voila, you have a pair of male and female MC 4 wires on your panel. At unlimited-solar.com, such a 6' in 12 ga costs $3.99, while 10 ga. costs $4.99.
