The type or namespace name `ParseObject' could not be found. Are you missing a using directive or an assembly reference?

test.SaveAsync ().ContinueWith(t=>);

ParseUser.LogInAsync("myname", "mypass").ContinueWith(t =>
{
     if (t.IsFaulted || t.IsCanceled)
     {
         // The login failed. Check the error to see why.
     }
     else
     {
         // Login was successful.
     }
})

LoadLevelAsync can only be called from the main thread.
Constructors and field initializers will be executed from the loading thread when loading a scene.
Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.

using UnityEngine;
using System.Collections;
using gui = UnityEngine.GUILayout;
using System.Threading.Tasks;
using Parse;

public class Register_and_login : MonoBehaviour {
     public string _password = "";
     public string _username = "";
     public string EmailPole = "Email";
     public string NamePole = "Your Name";
     int RegisterButton = 1;
  int MenuButton = 1;
   
   
  void OnGUI() {
   if (MenuButton == 1) {
   gui.Label("Register");   
   gui.Label("Profile");
   _username = GUILayout.TextField(_username);
      _password = GUILayout.PasswordField(_password, '*');
   if (gui.Button("Login")) {
    ParseUser.LogInAsync(_username, _password).ContinueWith(t =>
{
     if (t.IsFaulted || t.IsCanceled)
      {
         Debug.Log ("Error 404");
     }
     else
     {
        Debug.Log ("LoginComplite");
     }
});
   }
   if (gui.Button("Register")) {
     var user = new ParseUser()
{
     Username = _username,
     Password = _password
};  
    Debug.Log ("RegisterComplite");
      
     }
    }
      }
      
  private void Register(){
  var user = new ParseUser()
{
     Username = "Name",
     Password = "Password",
     Email = "email@example.com"
};
   
// other fields can be set just like with ParseObject
user["phone"] = "415-392-0202";
   
Task signUpTask = user.SignUpAsync();  
}
   
  private void Login() {
   ParseUser.LogInAsync(_username, _password).ContinueWith(t =>
{
     if (t.IsFaulted || t.IsCanceled)
      {
         Debug.Log ("Error 404");
     }
     else
     {
        Debug.Log ("LoginComplite");
     }
});
  }
   
  private void CurrentUser (){
  if (ParseUser.CurrentUser != null)
{
     // do stuff with the user
}
else
{
     // show the signup or login screen
}
  }
   
}