A quick handy reply to your question dsdisciple!
The four emanations correspond to the four energies; and in total, the five forms of Dorje Shugden correspond to the five buddha families (and their energies). you can also identify this by their colors:
Shize (white): peaceful emanation (for healing, pacifying serious illnesses or natural calamities in certain areas)
Gyenze (yellow): the emanation for increase (increase of wealth, resources, attainments, dharma teachings and wisdom)
Wangze (red): control emanation (for taming very difficult minds, bringing peace and calming people with very difficult minds).
Trakze (dark red): wrathful emanation (for protection against or combatting very serious negative inteferences or disturbances)
If you are unsure which emanation you should do, the best would be to seek the advice of your teacher or, if you are not able to, recite the mantra and do the prayers of the main form of Dorje Shugden, is encompasses all.