|In most cases on modern computers, the speakers must be amplified speakers if you're connecting them to the onboard audio. If your computer is an exception to that, there would be info about that in the Owner's or User's manual for the specific model.|
"There are 6 jacks on the back"
For the onboard video, probably....
Green = a single pair of speakers (stereo) or Front pair
Pink = Mic in - mono, or sometimes stereo (always)
Blue = Line in, or in some cases can alternately be used for a speaker pair (8.1 sound)
Orange = Center speaker or Subwoofer
Black = Back pair
Gray = Sides pair
The speakers in the monitor are probably amplified by circuitry inside the monitor.
If the computer has an audio card installed in a mboard slot, there would be ports for that farther down on the back of the computer in a slot space by themselves, depending on the model of it, it MIGHT have a amplifier on it and an additional jack you can plug an un-amplified speaker pair into.
If you DO have an audio card in a slot space, the audio adapter you have installed the drivers / associated software for last becomes the default sound adapter Windows uses. You can change that in Control Panel ( Classic view) - Sounds and Audio Devices - Audio tab if you need to.
I don't know of any set of speakers that has more than a pair of speakers that has a subwoofer that does not have an amplifier inside the subwoofer box that must be connected to AC or an AC to DC adapter.
If you want to connect more speakers than one pair, for the onboard video, you have to go to Control Panel (Classic view) - the icon for the brand of the sound adapter - and change a settuing from the default one pair of speakers to however many speakers you want to connect.