If your form fields include an input for file uploads, FieldGoal will store these files to S3 once configured. You must have an Amazon S3 account setup with programmatic access, along with a bucket and directory that you want to use for file uploads.
Navigate to FieldGoal's form settings page and add your S3 access keys. Please note that your Secret Access Key can only be downloaded once it is created. If you no longer have it, you will need to create a new one.