What is the conflict of the book called Matilda?

The theme of Matilda is, quite simply, goodness overcomes evil.

Matilda Wormwood is a small child with great intelligence. Left to her own devices, she teaches herself to read, and despite being denied books at home, she begins visiting the local library daily, poring through all the books. When the kindly librarian gives her a library card of her own, there is no stopping Matilda in her quest for learning.

Mr. Wormwood sells used cars for a living, but he cheats his customers with poor quality cars and shoddy workmanship. He sells a car to Miss Agatha Trunchbull, the principal of Crunchem Hall, a private school. During negotiations, he arranges to enrol Matilda in the school. Matilda discovers that Agatha Trunchbull is a terrible tyrant, punishing the children at the school for tiny misdemeanours. Meanwhile, Matilda's intelligence also impresses her lovely teacher, Miss Honey (who happens to be Trunchbull's niece), so much that Miss Honey regretfully suggests to Miss Trunchbull that Matilda should be progressed to a higher grade. No other adults - least of all Matilda's parents - seem interested in Matilda's vast intellectual capacity.

At one stage, Matilda's anger at her parents causes her to discover that she has the gift of telekinesis, that is, being able to move things by the power of her mind. Newly armed with this gift, she teaches both her family and Miss Trunchbull some unforgettable lessons. She frees Miss Honey from the abuse she has suffered all her life at the hands of Trunchbull, and ends up living with Miss Honey.