Radha Krishna
In Sanatan Dharma, as explained in the Bhagavad Gita, there is only one Supreme God. However, the Lord expands Himself as incarnations and avatars, and descends to our material world in order to conduct His missions.
Śrī brahma-saṁhitā 5.1
īśvaraḥ paramaḥ kṛṣṇaḥ
sac-cid-ānanda-vigrahaḥ
anādir ādir govindaḥ
sarva-kāraṇa-kāraṇam
ईश्वरः परमः कृष्णः सच्चिदानन्द-विग्रहः
अनादिर आदिर गोविंद: सर्व-कारण-कारणम
Krishna who is known as Govinda is the Supreme Godhead. He has an eternal blissful spiritual body. He is the origin of all. He has no other origin and He is the prime cause of all causes.
Radha Krishna
In several important scriptures (Bhagavad Gita Srimad Bhagavatam and Brahma Samhita) Krishna is referred to as Svayam Bhagavan, the original Supreme Personality of Godhead.
Radha is the primeval potency of the three main potencies of the Lord, Hladini (immense spiritual bliss), Sandhini (eternality), and Samvit (existential consciousness), of which Radha is an embodiment of the feeling of love towards Krishna (Hladini).
With Krishna, Radha is acknowledged as the Supreme Goddess. Krishna is said to be satiated only by devotional service in loving servitude, personified by Radha. Various devotees worship her to attain Krishna via her. Radha is also depicted to be Krishna himself, split into two for the purpose of his enjoyment.
It is understood that Krishna enchants the world, but Radha enchants even him. Therefore, she is the supreme goddess of all, and together they are called Radha-Krishna.
Krishna, together with Radha, descended to Earth in His original spiritual form and performed magnificent and sweet pastimes for the pleasure of His devotees.
Resources:
- The appearance of Krishna https://youtu.be/teM1lQ5xMZA
- The appearance of Radha https://youtu.be/2gwpU234eXY
- Inauguration of Radha Krishna on Shree Krishna Janmastami 19.08.2022 https://youtu.be/9YaY2SX_4L0