Important/main events are actions which drive the plot and highlight the main themes in a work of fiction. There are usually four main story structures that are common in fiction, namely the milieu story, the idea story, the character story, and the event story. Read about them here.
The event story is what we're interested in here. Most fantasy and science fiction stories use the event story. In such a scenario, the world is in deep crisis, while a new order waits in the wings for its moment to act. In the event story, authors don't usually spend much time delineating the background of the protagonist for the reader. Instead, the reader is often plunged right into the action, into the crucial moment the protagonist joins the struggle against the threat. The main events which drive such a plot will focus on the protagonist racing against time to restore or usher in either a new order of things or maintain the old order of things.
So, to identify main/important events in Cinder, we have to keep in mind that Cinder Linh is living in the middle of a crisis in her world: a strange plague (letumosis) threatens the lives of her people, while an ambitious Lunar race watches over Earth and its resources greedily. Thus, the main/important events would center on how Cinder becomes embroiled in actions which cement her place in the crisis, her continued involvement in the affair, and her eventual emergence as the one character who can save her world.
Marissa Meyer's Cinder is the first book of her Lunar Chronicles series. So, the story doesn't end in this book; Cinder's pivotal role in the race to prevent Earth from being enslaved by Queen Levana continues in subsequent books. All the Lunar Chronicles books represent a modern retelling of an old fairy tale. Cinder mirrors the Cinderella story. As in the Cinderella story, the step-mother and step-sisters are crucial in propelling Princess Selene/Cinder into the arms of the handsome Prince (in this story, Prince Kai.) Now that we've established how to identify important events in an event story, here are brief summaries of some main events:
1)Cinder's first meeting with Prince Kaito (Kai) occurs when he tasks her with fixing his android, Nainsi; Cinder is a mechanic. This first meeting establishes the two main characters in this novel. Prince Kai is not only the Prince of the Eastern Commonwealth, he is also deeply involved in ongoing letumosis (The Blue Fever) research and the quest to find an antidote/vaccine. Prince Kai's father, the Emperor Rikan, is himself stricken with the plague. When the marketplace where Cinder works is evacuated due to a baker (Chang Sacha) contracting letumosis, we are introduced to the crisis that is plaguing Earth.
2)Peony, one of Cinder's step-sisters, contracts the deadly plague, which has never been known to leave a survivor. Due to this, Peony is picked up by androids at the Taihang District junkyard and taken away to the quarantines. Linh Adri, Cinder's stepmother, blames Cinder for Peony's plight because of her proximity to Chang Sacha at the marketplace. An important fact has been established here: Cinder herself does not contract the plague and neither is she a carrier for the disease.
3)As revenge against Cinder for supposedly causing Peony's infection, Linh Adri volunteers Cinder for plague research. This is how Cinder makes the acquaintance of Dr. Erland, a palace researcher who is a crucial supporting character in the story.
4)At the research facility in the palace, we learn that Cinder is a cyborg who has a control panel, synthetic hand and leg, and a computer chip plugged into her nervous system. She is also discovered to be 36.28% not human. As a volunteer (albeit, forced) Cinder is injected with letumosis microbes, but she is shown to be immune to the plague. Her conversation with Dr. Erland establishes that she was supposedly brought to the Eastern Commonwealth by her step-father, Linh Garan, after a supposed hovercraft accident killed her parents when she was eleven.
5)Prince Kai runs into Sybil Mira, Queen Levana's head thaumaturge, on his way to see Dr. Erland. This meeting establishes Queen Levana's business with Prince Kai and his people. She wants an alliance with Earth and aims to fulfill her wishes through Prince Kai now that the Emperor is stricken with letumosis. Kai's discussion with his advisor, Konn Torin, introduces the missing Princess Selene, supposed heir to Queen Levana's throne. We learn that Princess Selene is rumored to have died at three years old in a fire; only her hand and foot were ever found. She is rumored to be hiding on Earth. Kai wants to find her to help thwart the ambitious Levana's plans to subjugate Earth and her people.
6)Prince Kai meets Cinder, this time, at the research facility. This meeting further solidifies the couple's budding romance.
7)Emperor Rikan dies and Queen Levana wants a marriage alliance with Prince Kai. She is coming to New Beijing to see the alliance through.
8)Prince Kai asks Cinder to go to the ball with him, but she declines. Dr. Erland warns Cinder to get away before Queen Levana comes to the palace for her meeting with Prince Kai. Dr. Erland reveals to Cinder that she is of Lunar blood and Lunarians are natural carriers for the disease. This explains Cinder's immunity to the plague. Dr. Erland also reveals that many Lunar parents secretly sent their children to earth to escape the infanticide laws under Queen Channary, Princess Selene's mother. Dr. Erland tells Cinder that Queen Levana would kill her if she knew of her existence.
The above is an example of main events in the story. Remember to also include Cinder's discovery of who she really is and her eventual partnership with Dr. Erland to fight the Lunar powers under Queen Levana.