There are many bahrmanas (parts) in each chapter. Each of the brahmanas has a particular name also. The name reflects the message included in that part. In the first chapter of brauhadaaranyaka Upanishad, the descriptions go like creation of seven horses of sun (aswa ulpatti brahmana), the formation/ creation of sun (aaditya srushti brahmana), creation of this world from the sun ( Jagath srushti.) , formation of the earth from the sun ( bhoo srushti)... description of jeevaathma.., paramaathma, what is meant by asura and deva, in its philosophical meaning, creation of the living beings, creation of man, formation of dharma for men, both varna and asrama dharma, the relation among pancha jnaana indriyas, pancha karmendriyas, pancha praana, pancha bhootha.. the relation between vaak and mana ( speech and mind), detailed description of brahma chaitanya / brahmam.
This Upanishad gives an abstract of the deep message on the absolute truth / fact /essence of the world and its manifestation as everything in the world ( the theory of everything or M theory). For an in-depth understanding one needs to study the commentary of the Upanishads written by great modern and ancient Rushies..