Your original text is mostly clear, but I have noted a couple of grammatical corrections:
- Change "make a text more interesting and more descriptive" to "make a text more interesting and descriptive." (Removed the second "more" for conciseness)
- Change "make it so the reader can picture what the author is trying to say more clearly" to "make it so that the reader can picture what the author is trying to say more clearly." (Added "that" for grammatical correctness)
Revised text with changes:
"The purpose of figurative language is to make a text more interesting and descriptive. An author might use it in their writing to engage the reader in their story and make it so that the reader can picture what the author is trying to say more clearly."
Additionally, consider changing "in their writing" to "in his or her writing" for greater formality, but this is a matter of stylistic preference, not a grammatical error.