Hey Bacon and welcome to the community 
Don’t know if it’s the combo or head…
This jack plug is your combo’s speaker cable, it connects from your amps output to the speaker. So you need to do the following:
- Unplug all power from the amp and Power Station.
- Unplug your speaker cable – remember this jack socket, we need it for later…
- Use a 1/4" jack female to female coupler
- Connect the female coupler to the jack you just unplugged.
- Connect a speaker cable from the coupler to the Power Station SPKR OUT
- Connect a second speaker cable from the Power Station AMP IN to the jack socket from step 1.
- Match the impedance settings between your amp and the power station.
- Done
For your other question take a look here,
Hope that helps!
Regards,
Dan