I guess, for slot filling feature, following link might help you out:
https://api.ai/docs/examples/slot-filling
Now the answer to your previous question where you asked, how to call webhook on specific intent only after setting required parameter true. Please have a look at following snap wherein you have an option to set "required" for any parameter in action & "use webhook" in fulfillment. So now webhook will be called only for that specific intent when that parameter value is entered by user such as UserEmail in the following snap.

Now if you want to use this "email" value in your webhook, you just have to create a class for get & set method:
public class Parameters
{
public string UserEMail { get; set; }
}
& use this value to respond user
case "Ask For Email":{
string strUserEmail = request.result.parameters.UserEmail;
obj.speech = "Thank you";
}