Sorry because I can't use Chinese and my English is kind of terrible.
ふりがな is written down in order to help you read hard Kanji(s). It is かな over or beside kanji to indicate pronunciation.
In a sentence, like 「私（わたし）は日本語（にほんご）が苦手（にがて）です。」、「わたし」「にほんご」 and 「にがて」 are ふりがな because they help you read those kanji(s). They are also かな because they are ひらがな. 「は」「が」 and 「です」 are not ふりがな because they don't indicate pronunciation of any kanji(s) but they are still かな since they are still ひらがな.