There's not much that can be said publically--Khacho Karmo is not really suitable for public discussion. It is one of the penultimate Five Golden Dharmas of the Shangpa Kagyu. Here's what I can tell you: The lineage comes from Atisha, amongst others, through Niguma and then through the Shangpa lineage. The practice involves supplications and special yogic practices, relating to Bliss/Emptiness and the four joys, and the completion stage practice is a sort of Phowa, allowing one to travel to the Pure Land of the Dakini.
This practice, as well as the Red One (Khacho Marmo), are known as the two "flowers" of the Shangpa tree. The roots are the Six Yogas of Niguma, the trunk is Mahamudra of the Amulet box, the branches are the "Three Carryings on the Path," the flowers are the two dakinis, and the fruit is Deathlessness of Body and Deathlessness of Mind, also sometimes referred to as "Non-Entering of Samsara and Nirvana."
Prior to practicing this, you would normally have completed ngondro, extensive yidam practices, the Six Yogas of Niguma, and be involved in Tantric Mahamudra practice, in retreat.