How to use TDD to test a process?

I try to use stub but it seems not very good. I want to know how should I write the test case, and how many should it be? Could someone help me? Thank U!

 logic like this:
 

 public class User
 {
     public int ID
     {
         get;set;

     }

     public String Name
     {
          get;set;

     }
     public String BrokerID
     {
          get;set;

     }
     public String Timestamp
     {
          get;set;

     }
 }

 

 public interface IUserDao
 {
     User GetUser(string userID,string brokerID);
     bool Save(User user);
     bool Delete(User user);

 }

 

 public UserService
 {
     private  IUserDao _userDao;
     public UserService(IUserDao userDao)
     {
           _userDao=userDao;

     }
     

    public bool Record(User user)
    {
          User origin=_userDao.GetUser(user.Name,user.BrokerID);
 

          if(orign)
          {
             if(!_userDao.Delete(origin))
             {
                    return false;

              }
          }
 

          if(!_userDao.Save(user))
          {
                   return false;

         }   
         return true;  
    }

 }