Baybayin was syllabic in nature, meaning that each character represented a complete syllable, rather than a single sound, as represented by a letter in the modern Filipino alphabet.
Baybayin was used primarily in Luzon and the Visayas.
People in Mindanao primarily spoke Arabic, after the Islamic conversion, by the time the Spanish arrived, and Baybayin was largely forgotten in Mindanao (If you are a Muslim, you must be able to read the Koran, which is only officially written in Arabic).
Many Friars noted with pride their destruction of “pagan” documents written in Baybayin, and most of the documents written by the ancient Filipinos were lost forever.
However, as this article noted in the beginning, “History is written by the victors”, and the Spanish used language as a means of control.
For the sound “O” or “U”, the kudlit is written below the symbol.