"How do Christians believe in God?"

Christians believe in one God who created Heaven and Earth. They also believe God is one being who is also 3 persons, The Father, The Son and The Holy Spirit.

"How do Sikhs believe in God?"

Sikhs believe in one singular God who has no gender lives on forever. Sikhs refer to God as Waheguru. A core belief of Sikhism is rebirth and karma, so they believe in Waheguru to reincarnate them.