What is God in Dharmic understanding?

God = The Absolute Reality

But how is it divided and how to understand it? I'll try to explain.

Brahman: In Hinduism, Brahman is the name for the Absolute, the Supreme Reality in the universe. It is the immaterial, efficient, formal and final cause of all that exists. It is also understood as the ultimate reality and the basis of everything.

There are two main forms of Brahman: Saguna Brahman and Nirguna Brahman, which I will explain below.

Param Brahman: Param Brahman (or Para Brahman) is the "Supreme Brahman" in Hindu philosophy, which is beyond all descriptions and conceptualizations. It is described as a formlessness that eternally pervades everything, everywhere in the universe and what is beyond. He is also known as Nirguna Brahman.

Nirguna Brahman: Nirguna Brahman refers to the concept that Brahman is beyond time and space. It is the idea that Brahman has no concrete form and is present in all living beings and everywhere, that is, it is transcendent and beyond human understanding.
In the Advaita Vedanta tradition, it is synonymous with Param Brahman and is known as nirguna brahman, the Absolute without attributes and form.

Saguna Brahman: Saguna Brahman is Brahman with form, identity and purpose that can change with time. In the Dvaita Vedanta and Vishistadvaita Vedanta traditions, it is a form of Param Brahman and is defined as saguna brahman, the Absolute with attributes, which manifests itself to humans through divine forms (deities).
This form of Brahman is often associated with specific deities such as Krishna and Vishnu in Vaishnavism, Shiva in Shaivism, and Durga or Adi Shakti in Shaktism.

Bhagwaan is a term used in Indian religions to refer to figures of religious worship ( = personalised deities). Bhagwaan literally means "the one who is worshipped". In Hinduism, it is used to refer to a deity or avatar, especially Krishna and Vishnu in Vaishnavism, Shiva in Shaivism, and Durga or Adi Shakti in Shaktism.

Avatar is a term used in Hinduism to refer to the earthly incarnation of a deity.

Murti: is a representation (statues, pictures) of Bhagwan (deity) who is a manifestation of Brahman (Absolute = God). So, when Hindus worship Murti, they worship Bhagwan through him and ultimately Brahman. In this way, the Murti is the instrument that enables the devotees to connect with Brahman through Bhagwan.

Atman: is a term used in Hinduism to refer to the individual soul or self. Atman is understood as the immortal self, which, according to Advaita Vedanta, is essentially identical with the transcendental Brahman.

Aum: (is pictured) symbolizes the infinite Brahman (Absolute = God) and the entire universe.
Aum is a sacred syllable known from the Vedas and is considered the most sacred syllable in Sanathan Dharma (Sanathan Dharma = "Eternal Dharma", and it´s the original name of Hinduism). The syllable Aum is found in both Hinduism, Jainism, Buddhism and Sikhism. Numerous Hindu texts and mantras begin with this syllable.
Also, the Sikh Dharma (Sikhism) uses the words Aum as the name of a single deity.

And something more about the Bhagwans (deities):

Deva (in Sanskrit देव déva "heavenly, divine") is a designation of deities in Hinduism. A large number of devas were worshiped in the Vedic religion, where they were central objects of worship. In later Hinduism, they became more like subordinate beings to the supreme being.

Devi (in Sanskrit देवी, f., devī, "goddess") is a Sanskrit term for any goddess in Hinduism. Among the most famous are, for example, Sarasvati, Kali, Lakshmi or Parvati. Goddesses are worshiped primarily in Shaktism.