I probably should, but the basics of Manifestation is pulling forward your Demonic Traits by 'Synchronising' with your Demonic Energy. It's basically a Mental command/state which allows you to become more in tune with your Demonic Form. Partial Manifestation is pulling forward Demonic Traits in a body part only (An arm, a Leg, or your wings/tail, for example) while Full Manifestation is pulling them forward in your entire body. The % rates are roughly defined as this; 1-10% general enhanced skills (Even more than the passive boost you get) 10-50% minor demonic traits, loss of control (Enhances skills even more drastically, but causes slight loss of control and causes most demonic features to come out (Eyes, skin color, hair color, other features (Tails, horns, wings etc)) and then 50-100% increased loss of control, berserker features, full Demonic Traits. (As you get closer to 100% your form becomes increasingly closer to your Demonic Form, and you lose control to the point where it becomes hard to distinguish friend from foe.)
Of course, a lot of the control aspects can be negated with training. Also, something I just thought of; Every Half-Demon has some sort of Limiter (Magical Sealing Tattoo) inked on their body which allows them to gradually increase their synchronisation. Only those with exceptional willpower could pull out partial demonic traits on their own. (Basically, the Limiter allows you to only partially use your Demon Form, rather than just going 100% straight away.)