It was easier to write Japanese with Manyogana than with exclusively Chinese logograms, but it was still difficult because the same glyph would represent a word in one place and a sound in another. For their next attempt, the Japanese kept the idea of Manyogana, but used slightly different versions of the glyphs. It was probably easier to make simpler versions of the glyphs than more complex ones, and that’s what they did. Hiragana was the result; the Hirigana glyphs are generally a sub-element of the corresponding cursive Manyogana glyphs.
At first, Hiragana was mostly used by women, who were not taught Chinese characters. Eventually, the guys figured out that it was a lot easier to use Hiragana than Manyogana. Today, Hiragana is widely used in Japan for Japanese words that don’t have logograms, pronunciation, and Japanese inflections (i.e. “sounds stuck onto words to change their meaning slightly”, like “-ing”, “-ed”, or “-s” in English).
Just as people used several different glyphs in Manyogana to represent the same syllable, people used to use several different glyphs in Hiragana to represent the same syllable. In 1900 AD, the government rolled out some spelling reforms that included one approved glyph shape per syllable, but you still see it some glyph variants (called Hentaigana) used from time to time to evoke tradition.
Hiragana has two decorations for its syllables which change its consonant in predictable ways. The first is the dakuten, which looks like a double-quote (visible on today’s glyph), which changes the consonant from unvoiced to voiced. (The difference? You can put a musical note on a voiced consonant, but can’t on an unvoiced; you can whisper an unvoiced consonant but not a voiced one. “S”, “k”, and “t” are unvoiced, for example; “z”, “g”, and “d” are their voiced counterparts.) The other decoration — a small circle — changes the sound from a “h” to a “p”. These decorations became standard somewhere between 1600-ish and 1800 AD-ish; before then, Japanese did not distinguish between the sounds.