Pottermore was a website that was discontinued in 2021. It allowed users to read the Harry Potter books, take quizzes, explore the wizarding world, and even create their own wizarding character.
However, there was no system in place to "earn" spells. The spells you had were determined by your House and your progress through the website.
If you are interested in learning more about spells in the Harry Potter universe, you can check out the Harry Potter Wiki or the books themselves.