Every member of the nation - men, women and children - were commanded to assemble at the Temple on the second day of Succos in the year after shemittah in order to hear the king read certain passages from Deuteronomy. This mitzvah is called hakheil, the assembly. (This mitzvah is an exception to the normal rule that women are not obligated in positive mitzvos that must be performed at a specific time.)
A Torah scroll was passed from the gabbai of the Temple synagogue to the head of the synagogue to the deputy High Priest to the High Priest to the king. The king read seated on a large platform assembled in the women's court of the Temple. (The mishna in Sotah – 7:8 - tells us that King Aggripas stood, for which he was praised by the Sages.) He started with the usual blessing before reading the Torah and he followed his reading with seven blessings.
The reason for this mitzvah is that Torah is the heart of the Jewish people. This sets the nation apart from all others. It is only appropriate that the entire nation should gather together periodically to hear words of Torah from the mouth of the king, serving as a reminder of this significant reality.
This mitzvah applies to both men and women at a time when the Jews reside in their land. It is discussed in the Talmud in tractate Sotah (41a-b). It is codified in the Mishneh Torah in the third chapter of Hilchos Chagigah. This mitzvah is #16 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.