The energy-principle that is Pluto is power and deep psychism; intensity and rebirth, or negatively: control and abuse.
People with unaspected Pluto in their birth chart can come over very powerful to others and not know it; or they can be unable to access their power and even be abused. And both of these can be true at different times in the life.
It is a good start to approach Pluto through contact with his myths:
The Pluto – Persephone: Pluto Myth 1
This is really important key to understanding the energy of the planet Pluto. Persephone was an innocent girl picking Narcissi in the fields. Pluto, the Dark Lord, Lord of Hades desired her. The earth gaped at her feet and a chariot drawn by black horses breathing fire erupted from the depths. The God swept her into his arms and took her to his own dark realm and said he would make her his Queen. So, by transforming sexually, Persephone came into great power and became Queen of the underworld. But her mother, Demeter, the Earth Goddess, mourned and missed her daughter, to such an extent that Demeter ceased from her work of fructifying the Earth. Nature began to die. Humanity faced annihilation.
And so, the humans petitioned the Gods who sent Mercury to do a deal with Pluto, the upshot of which was that Persephone would only reign in Hades half the year, but could return to her mother Demeter the other half. So, while her daughter is Queen in Hell Demeter still mourns, and it is winter – but for the other half of the year, Demeter has her daughter back and it is summer.
And the point is that there are immense buried riches and power to be found in growing and transforming and contacting the underworld of the unconscious. The only way Persephone could transform was by being abducted to meet her destiny.
But Pluto is not only power and transformation; it is deep psychic perception and intuition.
Unaspected Pluto people usually had to learn very early on that things were not as they might seem in the home.