We have been wandering in delusion in samsara since beginningless time, like being trapped in a dream. The dharma is the method that the Buddha taught to wake us up from this dream. For that purpose he taught the 84,000 teachings of the dharma for beings of lesser and medium capacities, and the 6,400,000 tantras for disciples of the highest faculties. They all have one purpose, to tame the five passions of desire, anger, ignorance, jealousy, and pride in each individual being’s mindstream. The teachings are extremely vast, but the condensed essence of all of them, the pith instruction that encompasses all spiritual traditions, is Ngondro. ~ HH Dudjom Rinpoche

All Buddhist and non-Buddhist spiritual traditions see samsara as not a good place to remain and seek to end suffering according to their own capacities and methods. The outer preliminary practices are the four ways to turn the mind to dharma and away from samsara (four thoughts).

The inner preliminary practices begin with going for refuge, the foundation of the path of liberation from Hinayana through Vajrayana. The essence of the path from Mahayana through Vajrayana is to arouse in the mind the thought of supreme enlightenment, Bodhicitta.

In order to attain enlightenment we need to perfect the two accumulations, and mandala offering is the method to quickly accomplish this. The outer mandala offering is the billionfold universe, the inner mandala offering is one’s own body, enjoyable possessions, and accumulations of virtue, and the secret mandala offering is the Dharmadhatu Clear Light Vajra Essence Buddhafield. Actually, everybody needs to accumulate merit, it is not just for those who want to attain Buddhahood. It is the foundation of all worldly happiness, and it gathers the favorable circumstances for attaining enlightenment.

In order to purify unfavorable circumstances we do Vajrasattva meditation. It is a complete tantric practice that includes shamatha and vipassana according to the Vajrayana tradition of the two stages of creation and completion.

Guru yoga is the heart of all practices in the Great Perfection tradition which is the essence of all dharmas and spiritual paths.

Ngondro also includes Phowa, a Great Perfection teaching for swiftly transforming consciousness at the moment of death, even if one dies before being able to accomplish the creation and completion stage practices.

Chod is the practice of severing all types of clinging such as the four maras which create obstacles to samadhi, wisdom, accomplishing meditation practice in this life, and attaining Buddhahood.

As Dudjom Rinpoche said,

This profound revealed treasure, this preliminary practice arra nged here, is the noble path which leads swiftly and easily to the level of the union of the Four Kayas;
It is a chariot, perfectly clear and easily entered, that is brought up here;
All fortunate ones, enter now with joy!