You have likely been told that characters in your story should want something, and it would be a frightfully dull novel if your characters got everything they wanted without any effort (or, as Agent Smith puts it in The Matrix: a dream our primitive cerebrums would keep trying to wake up from).
The duology of protagonist vs. antagonist provides your narrative with the conflict that keeps readers up way past their bedtimes, wondering if your main character will succeed. Your protagonist wants something, and wants it deeply, and your antagonist stands in their way. This opposition drives your story.
This blog post, written for The Novel Factory will help you understand what the roles of protagonist and antagonist mean for your story, and offer suggestions to make your protagonist and antagonist stronger.