I need to write an essay on chapter 1 ("The Veil"). It should be no more than 500 words.

You might want to start by researching the 1979 Islamic Revolution, which brought to power Ayatollah Ruhollah Khomeini as the Supreme Leader of Iran. It was Ayatollah Khomeini who decreed that all women must wear the veil. You might want also to research the significance of the veil in the broader context of the Muslim religion. I have provided a link below that you could use to get started.
Next you might want to consider what we learn about Marji when she was younger, including how her parents brought her up. She wanted to be a prophet. She had sympathy for women, like her family's maid and her grandmother, who she thought should have been treated better. Her parents sympathized with her ambitions to change things and altogether seem like they were quite liberal parents. With all this in mind, you might explore how Marji is likely to respond to the decree that all women must wear the veil and, indeed, to Ayatollah Khomeini's rule in a broader sense.
Another potentially interesting approach to chapter 1 might be to consider the tone of the story. The story opens, for example, with rather serious issues, such as the revolution and the decree that women must wear the veil, but then in the flashback to Marji's childhood, there is an element of humor, largely because the story is filtered through a child's perspective. It might be worth considering what kind of tone you think Satrapi is trying to create and how suited you think this tone is to the issues being explored.
https://www.bbc.co.uk/news/world-middle-east-47032829