How to manage multiple classes using a web service?

I am creating a web service in asp.net. I am not getting which one is best to manage multiple classes using a web service.

Two ways in my mind, but I don’t understand which one is better.

1) Calling all classes in a single .asmx file. 2) Create another .asmx file for all classes.

paypal.sandbox.AddressType addressType = new paypal.sandbox.AddressType();
    addressType.AddressID = "Your Address ID";
paypal.sandbox.DoDirectPaymentResponseType response = new paypal.sandbox.DoDirectPaymentResponseType();
    response.TransactionID = "25554d";

I want to call my classes similar from my code. I do not understand how this can be called. Please help me solve this problem.

thank