If you were going to explain Dharmakāya to someone who has never encountered the topic prior, where would you begin? Dharmakāya is tricky business to explain.  

If you were to explain it to someone who has never heard of the concept where would you begin? 

How does it fit in with attraction and aversion?   

At the same time the explainer would have to make sure to cover the different ways the word Dharmanakaya has been used.
Although the notion appears in all sorts of philosophical treatises, as well as in tenets, it is explained at length in texts expounding 'buddha nature' (tathagatagarbha). I would recommend in particular the study of Maitreya's 
Uttaratantra Shastra (Treatise on the Sublime Continuum). Although it is called 'uttara-tantra' it is included within the perfection vehicle (sutra). Maitreya's Sublime Continuum has been commented upon by various scholars of different traditions, and so there are various interpretations.

From the point of view of the cause, the general presentation is that from the accumulation of merit, one achieves the form body (rupakaya) of a buddha that fulfill others' wishes, while one obtains the truth body (dharmakaya) from the accumulation of wisdom. The truth body fulfill one's wishes. The form body is divided into the one that is so subtle that it is not seen by ordinary beings (the enjoyment body) and a grosser one that ordinary beings can see (the emanation body). It is said that Shakyamuni Buddha was a supreme emanation body (a division of emanation body) endowed with the marks and signs. As this position no longer holds when we divide the bodies of a buddha (into three, four, or five as you will see bellow), it is merely the general presentation.

From the point of view of the result, the nature truth body (part of the dharmakya) results from the naturally abiding linage while the wisdom truth body (part of the dharmakaya) results from the developmental linage. Although we say that the nature truth body (suchness without defilements) results from the naturally abiding linage (suchness with defilements), it is not caused because suchness is permanent. Suchness with defilements is not an actual cause but a terminological division.

From the point of view of the nature, the general presentation identifies 'emptiness with defilements' to the tathagatagarbha and 'emptiness without defilements' to the dharmakaya. In this context, dharmakaya refers only to the nature truth body. Both are permanent and uncompounded. In Gyaltsab Je's commentary [to Maitreya], dharmakaya sometimes refer solely to the wisdom truth body or the nature truth body. It is where divisions are important. We can divide the bodies of a buddha in three ways:


The two bodies of a buddha
1. dharmakaya (truth body)
2. rupakaya (form body)
The three bodies of a buddha (it is referred  to as Trikaya)
1. dharmakaya
2. rupakaya divided in two:
--- 1. emanation body
--- 2. enjoyment body
The four bodies of a buddha 
1. dharmakya divided into two:
--- 1. nature truth body
--- 2. wisdom truth body
2. rupakaya divided into two:
--- 1. emanation body
--- 2. enjoyment body
The five bodies of a buddha
1. dharmakaya divided into two:
--- 1. nature truth body 
--- 2. wisdom truth body divided into two:
-------- 1. the omnscient mind that distinguishes conventionalities
-------- 2. the one that distinguishes the ultimate
2. the form body divided into two