Firebase Custom email verification

Question

I want to customize the email verification on firebase but I'm not sure how to.I understand that the documentation says "you must create and host a web page that uses the Firebase JavaScript SDK to verify the request's validity and complete the request" but I'm still having trouble. I created the handler on my website but my question is what do I do next? Can someone help me please?

auth_verify.js

function handleVerifyEmail(auth, actionCode, continueUrl, lang) {

  applyActionCode(auth, actionCode).then((resp) => {

   
  });
}