Re #3: I think you slightly misunderstood the teacher's instructions.
"On November 21st, I attended the famous Broadway musical ..." is not part of the summary of the piece. It is your introduction and should be in the past.
When talking about the plot or story of a book, film, play, etc. the common convention in English is to use the present tense. Beginning with "It is a story of being popular ...", you should use the simple present.
In the text below, if I add or change something, it will be in bold. If I have a comment about a change, I will put an asterisk in the text and then comment below. Neither the bold nor the asterisk should be carried over into your final version.
On November 21st,* I attended the famous Broadway musical Wicked in the Theater Telcel* in Mexico City. It is a story of being popular and being an outsider but also a story of friendship and love. The beloved* Glinda and the green-skinned Elphaba meet in school. Whereas Glinda is cherished, all the other students despise Elphaba. Through an accident, the teacher Madame Horrible recognizes Elphaba's extraordinary magical powers and tells her that maybe she can even work with the famous Wizard of Oz. One day, the* prince Friyero Fiyero?* arrives in the city, and Glinda immediately falls in love with him. Elphaba and Glinda become friends, and both go to the Emerald City, the home of the Wizard. Because of a magical spell, Elphaba puts all the monkeys in Oz in great danger. Although the Wizard tricked her, all the citizens of Oz, the witch hunters, now hunt her because she is perceived as the Wicked Witch of the West. Elphaba vows to fight the Wizard until the end. Fiyero and Elphaba both fall in love as well. Glinda, heartbroken and angry, frames Elphaba by telling her that her sister is in danger in order to catch her. After the death of her sister, Elphaba indeed becomes evil. However, she changes again when she and Glinda forgive each other. In order to live in peace and to* ensure her future with Fiyero, Elphaba convinces the witch hunters of her death. (or, "that she is dead.")
*In AE, you would normally write November 21, but November 21st is also acceptable. I don't know about BE.
*I disagree slightly with no me bré. The name of a theater does not have to be italicized, though it certainly may be italicized. In this case, I would not italicize it because of italicizing Wicked, which must be italicized because it is the title of a longer work. (Quotation marks are incorrect for the musical but would be correct for a song from the musical.)
*While "the beloved Glinda" is not wrong, "popular" is more current and probably reflects the situation. Someone can be "beloved" without being popular and vice versa. For example, in the title Cry the Beloved Country, it would be wrong to write "popular". Just how strong is opinion about Glinda? By the time of the original The Wizard of Oz, I would consider Glinda as definitely beloved and not just popular. In school, the situation may be different.
*Delete "the"; Prince Fiyero is title plus name, just like Mister Smith, Doctor Jones, so no "the". (In contrast, "the beloved Glinda" or "the popular Glinda" is fine because you are differentiating her from all other people named Glinda. However, California81 is correct that combining the ideas in one sentence will probably flow more smoothly.
*It looks like Friyero is a typo for Fiyero. I haven't ever seen Wicked, so I don't know which name is correct.
*Delete the repeated "to".
