They consist of hymns called Mantras which contain all knowledge in "seed" form (Bheeja roopa).
It is popularly believed (by scholars like Shankara) that Vedas consists of four parts – Vedas consists of Mantra Samhithas only, which believed to be Apourusheya (Sanskrit अपौरुषेय) – not of human origin but divine creation.
Brahmanas and Aranyakas are basically the same and Upanishads are written by sages (ancient scholars) as interpretation of Vedas.
The first time all four Veda Mantra Samhitas were printed with Swara-Sthana (punctuation for pronunciation) in Malayalam alphabets was the magum opus work of Narendra Bhooshan along with various studies on Vedic subjects.
The language of the Vedas is Vedic Sanskrit (1400BCE −300BCE )which uses special characters to give proper pronunciation.