Using fieldmaps & gradients with

Hello, I am very new to all of this. I wanted to reach out and ask for guidance/advice regarding incorporating fieldmaps that were collected into preprocessing my data, using This data uses a fear extinction paradigm, and so is event-based, though there is also some resting data before and after extinction. I was instructed to incorporate fieldmaps/gradients to make the preprocessing more robust, but I am 1) unsure exactly what fieldmaps and gradients are, and 2) am lost in terms of what they do to benefit data. If you can point me in a direction towards an article or something that would be super helpful!!!