What is a word to which letters or syllables are added to form new words

Ineed to write a write a 4–5 paragraph compare and contrast essay that addresses how anne frank matures over the course of writing her diary. it's also a compare and contrast essay i just got put into this new class and i don't know if we were supposed to already be reading and the essay is due today and i haven't even started it nor read the book, someone me what do i do