What's the different between kusala (good) and akusala (bad)? What's the different between ku-sala (good) and a-ku-sala (bad), in regard of what the Buddha taught?

(ku - bad, sala - cutting away, a - not)

What are good and bad actions by deeds, speech and mind, and what qualities defines them as such?

Here   he grieves
    he grieves  hereafter.
In both worlds
the wrong-doer grieves.
He grieves, he's afflicted,
seeing the corruption
    of his deeds.

Here   he rejoices
    he rejoices hereafter.
In both worlds
the merit-maker rejoices.
He rejoices, is jubilant,
seeing the purity
    of his deeds.
Yamakavagga

So good to now really good of how to distinguish and alltime worthy to ask, remember and tell for many's benefit, and the own.

(Note that this is not asked/given for trade, exchange, stacks or entertainment but as a means to escape this wheel here)
The explanation for Kusala can be found in MN-3 -&gt; Maha Chattarika Sutta ( I can't find this in english translation site, but this is in Sinhala / Pali Thripitaka ), So if I explain it how I understood by reading it,

It's about noble eightfold path, and in each it's describe two things one is lokottara (= focusing on Nivana) path the other one is laukika (= focusing on good things in this world: eg -&gt; samma kammanta = to do a decent job, not kill animals and sell).

And the opposite of this is Akusala which doing opposite things not knowing what the right view, resolve, speech, etc.. 

About lokottara path that person should have a correct view what is the problem with the world, why we are attached to things, and why we should not attached, what's the danger in that so on.

Hope my description led some lights and I should accept that I'm not a good translator.

Update:
Found more information on this. It's in Vibhangaprakaranaya-1, paticcasamuppada vibhangaya There you can notice what is kusala dharmayo, the explanation is given the paticcasamuppada cycle but it starts with sankara not with avijja that means when a thought is processed without avijja it causes to Nivana as it is a kusala