Asaph -
Mixer main out to sub input (A or B).
Sub output to line level input on your powered speakers. If you're using the A input, use the A output. If the B input, use the B output.
Set the HPF/Thru switch on your sub to HPF (for "high pass filter").
If you are going to be mono, connect the output of the powered speaker getting signal from the sub to the line level input of the other powered speaker.
Make sure that your mixer channels are panned to the output that you are using - if you are using the left main out, pan the channels left.
The signal from the mixer goes to the subwoofer first, because the subwoofer can then handle the low frequencies and pass only the mid and high frequencies to the main speakers - that is what the HPF (high pass filter) does when engaged.
So, Mixer to Sub to Mains. Got it?
As Mac requested yesterday, unless "Asaph Ace" is your real first and last name, go into your profile and use your real first and last name as your posting name, as required by the forum rules.
Oh, and buy some more XLR cables (or, better yet, learn to make your own)!
Good luck,
Pete