Kartini was born on April 21, 1879, into an aristocratic Javanese family with a strong intellectual tradition. At the time, Java was ruled by the Dutch colonial administration. Her father allowed her to attend school, where she learned to speak Dutch and she became an ardent reader. After withdrawing from school at the age of 12 to enter seclusion in accordance with the traditions of Javanese nobility, she corresponded with numerous friends abroad, read magazines and books, and ultimately rebelled against the strong tradition of gender discrimination and the restricted lives of Indonesian women.

        Through her letters, Kartini began a fight for the right of women to be educated and against the unwritten but all-pervading Javanese law, Adat. She came to view the feminist movement as a part of wider socio-political movement. She wrote passionately for the improvement of education, public health, economic welfare, and traditional arts in her country.
       She did not want marry but in 1903, consented to be the fourth wife of the Regent of Rembang, Raden Adipati Joyodiningrat, a man twenty-five years her senior. With her husband’s support, she obtained permission to open the first ever all-girls school for the daughters of Javanese officials, creating her own syllabus and system of instruction. By 1904, the school had one hundred and twenty students.

        Kartini died on September 17, 1904, following the birth of her son. After her death, Kartini's letters to her European friends were collected and published under the title "Out of the Darkness Comes Light".

       Kartini Day was established in 1964 by Sukarno, the first President of Indonesia and is held on the anniversary of her.

How do we celebrate Kartini's day?

1. All across Indonesia, female students and teachers in school are obligated to wear traditional costume (kebaya), while the male students dress in Batik.

2. There's a lot of competition you can join : fashion show, cooking, plating, and so on. (It depend on your institution).

Source :
https://encyclopedia2.thefreedictionary.com/Kartini
https://anydayguide.com