n00b alert: I am going through the graphql tutorial located here (hacker news clone): https://www.howtographql.com/react-apollo/6-more-mutations-and-updating-the-store/ I am creating a mutation:

mutation CreateVoteMutation($userId: ID!, $linkId: ID!) {
    createVote(userId: $userId, linkId: $linkId) {
      id
      link {
        votes {
          id
          user {
            id
          }
        }
      }
      user {
        id
      }
    }
  }

How does graphcool know what to do with

userId

and

linkId

in this query??