Hiragana is commonly used as an article in a sentence. The example, watashi wa nikki wo kakimashita in the image shows that the article “wa” is preceding the subject, watashi. The particle wo is preceding the noun nikki, which is the object that the subject, watashi, wrote.
There are some usages called furigana to assist in the pronunciation of particular kanji that have unusual usage or are rarely used. Furigana appears on top of these kanji, as the example in the image shows.
Another usage for hiragana is its application in Children’s (elementary school children) publications, including manga comics, children’s books, and school textbooks. These types of publications usually have furigana in any kanji. There is no kanji used in any books for children below the elementary level. Instead, hiragana takes place of kanji for very young learners.