All yidam practices, whether the deity is peaceful or wrathful, involve the generation stage. One cannot do deity practice without knowing how to practice the generation stage. To properly practice the generation stage in a retreat, one should first complete all the preliminaries, also pay particular attention to the process—there are many complicated requirements regarding the time, place, format of the retreat, and the time and format of ending the retreat, and so on. We don’t need to know the details for the time being, as many people have not yet undertaken the preliminary practice; even if some people have completed the preliminaries once, the quality of the practice is still less than satisfactory. However, the method of visualization is very important. If one is unable to visualize clearly, the entire result of practice will be adversely affected. The preliminary practices, such as the ones for taking refuge, Vajrasattva, and Guru Yoga, also entail the practice of the generation stage. Therefore, it is necessary to briefly explain this practice.
~Depicted from GATEWAY TO THE VAJRAYANA PATH - The Generation Stage