Who is Shrimati Radharani?

People, in general, do not know about Radharani. Radha-tattva is a very confidential subject matter which is hidden even from the Vedas. As a result, there are many misconceptions – or no conceptions at all – about Radharani. Radharani is a manifestation of Krishna’s love. Shri Radha is hladini-sakti, or the pleasure-giving potency of Krishna. Krishna is energetic and Radha is energy. Radha and Krishna are one Atma (soul) in the sense that they are Sakti (power) and saktiman (powerful). Even though They are one Atma (soul), still from time immemorial They have manifested in two different forms in Goloka Vrindavana to enjoy sweet pastimes.

Svayam Bhagavan Krishna has unlimited potencies categorized into three divisions: the internal potency, or antaranga-sakti; the external potency, or bahiranga-sakti; and marginal potency, or tatastha-sakti. The marginal potency is jiva-sakti. The external energy is the energy by which this material world is manifested, maintained, and annihilated. The internal potency is His potency by He maintains His spiritual world.

The internal potency, which is known as svarupa-sakti or cit-sakti, has three aspects. Sandhini-sakti is His aspect of eternal existence: the Lord’s existential potency by which He maintains His existence. The essential portion of the sandhini potency is suddha-sattva. Lord Krishna’s rests upon it. Krishna’s mother, father, abode, houses, bedding, seats and so on are all transformations of suddha-sattva.
Samvit-sakti is His aspect of cognizance or cognitive potency which is also accepted as knowledge, by which potency the Lord knows Himself and causes others to know Him. The essence of the samvit potency is knowledge that the Supreme Personality of Godhead is Lord Krishna.
Hladini-sakti is His aspect of bliss by which the Lord gets pleasure and devotees are nourished. By this He possesses transcendental bliss and causes His devotees to experience bliss.

Radharani is expressed as the expansion of the pleasure potency (hladini-sakti) of Krishna. As She is compared with the creeper, Her associates, the damsels of Vraja, are just like the flowers and leaves of that creeper. When Radharani and Krishna enjoy Themselves, the damsels of Vraja enjoy the pleasure more than Radharani Herself. Although the associates of Radharani do not expect any personal attention from Krishna, still Radharani is so pleased with Her associates that She arranges a meeting of Krishna and the damsels of Vraja, individually. By many transcendental maneuvers, Radharani tries to combine or unite the associates with Krishna. Radharani takes more pleasure in these meetings than in Her own affairs. And, when Krishna sees that both Radharani and Her associates are pleased by His association, He becomes more satisfied. Such association and reciprocation of love has nothing to do with material lust, but because it resembles such unification between man and woman, or the similarity to the combination of man and woman is there, therefore sometimes it is called, in transcendental language, transcendental lust.

Source: A.C. Bhaktivedanta Swami Prabhupada (2012 edition), “Teachings of Lord Chaitanya, The Golden Avatara”, Page 368 and 369
Bhakti Purusottama Swami (2008 edition), “The Glories and Pastimes of Srimati Radharani”, Page 19, 20 & 21