What is kana?
Before kanji, Japanese has two simple alphabets of sounds — called kana. They are the natural first step, the way Japanese children begin.
Two sets of sounds
Kana are phonetic: each character is just a sound, not a meaning. There are two sets. Hiragana (あ, か, さ) is used for Japanese words and grammar. Katakana (ア, カ, サ) is used for foreign and borrowed words. Both cover the same 46 basic sounds.
Kana came from kanji
Long ago, Japanese was written only with kanji borrowed from China. Over centuries, people simplified certain kanji into quick sound-symbols — that is where kana comes from.
A few kana and the kanji they grew from.
Why start with hiragana?
Hiragana is the foundation of reading Japanese. Once you can read its 46 sounds, everything else — katakana, then kanji — becomes much easier. So we start there.