When worried about vocabulary for an assignment, one option is to use words from the text to help. Remember not to plagiarize, but sometimes using words that the author presents in the text can help with a report. If you don't know those words, it is worth it for you to take a few minutes to look them up in a dictionary. (There are also online dictionaries you could consult.)
As far as the summary for each part of Fahrenheit 451, focusing on Montag and how he progresses or changes is a good idea because his actions and decisions move the plot forward. For example, in the first part of the novel, Montag is influenced by Clarisse and an old woman's suicide. He makes life-changing decisions based on these two events. First, he takes a sick day and wonders if he should quit his job; second, he learns about the history of the decline of literacy from Captain Beatty; and third, he chooses to read books and conduct his own research on the matter.
In the second part of the novel, Montag seeks out Faber, the old professor, to help him understand books. During their conversation, Montag gets the other side of the story of how literacy declined in their society. Then, Faber and Montag come up with a plan to sabotage the firemen by planting books in their homes. Unfortunately, Montag ruins those plans because he becomes agitated at his wife's friends and reads them poetry, and they all report him to the authorities.
By the third part of the book, Montag shows up to work as if nothing happened, hoping to continue with his plan to sabotage the firemen. But the damage has been done and Captain Beatty takes him along with the others to Montag's house to burn it down. Montag discovers that his wife reported him, and she leaves him without a good-bye. Tensions build between Beatty and Montag as the house burns down. Beatty taunts Montag to the point of madness and Montag kills him. In an effort to save his life from the Mechanical Hound which is soon to follow and kill him, Montag runs for his life. He deposits a book at the Black's house before he escapes the city by way of the river.
Once out of the city, Montag finds a hobo camp where people memorize books to keep them safe until society welcomes them back again. An atomic bomb levels the city and Montag grieves the loss of his wife. In the end, Montag heads towards the city to see what might be left of the civilization he once knew, with parts of Ecclesiastes memorized to share with someone else who might appreciate it.