ASP.NET Web Application C# multiple errors

I have multiple errors in my project, I don't know if i did it right, but i can't manage to solve them... some solutions?

using System;
using System.Collections.Generic;
//using System.Deployment.Application;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.Data;


namespace LoginApplication.Database
{
 public partial class DCApp
 {
  static DCApp __dc = null;
  public static DCApp GetDC()
  {
   {
    if (__dc == null)
    {
     return GetDC(true);
    }
    return __dc;
   }
   // end 
  }
  public static DCApp GetDC(bool reset)
  {
   if (reset)
   {
    if (__dc != null)
    {
     __dc.Connection.Close();
     __dc.Dispose();
    }
    __dc = NewDC();
   }
   return __dc;
   // end 
  }
  public static DCApp NewDC()
  {
   DCApp ndc = new DCApp(Globale.vgSQLDCConnectionString);
   ndc.CommandTimeout = 600;
   //if (!ApplicationDeployment.IsNetworkDeployed)
   //{
   // ndc.Log = Console.Out;
   //}
   //return ndc;
  }
  public static DateTime GetDate(DCApp _dc)
  {
   return _dc.ExecuteQuery<DateTime>("SELECT GETDATE()").First();
  }

 }
}

And here is the Error Log:

Error CS1061 'DCApp' does not contain a definition for 'ExecuteQuery' and no extension method 'ExecuteQuery' accepting a first argument of type 'DCApp' could be found (are you missing a using directive or an assembly reference?)

Error CS0161 'DCApp.NewDC()': not all code paths return a value

Error CS1061 'DCApp' does not contain a definition for 'Connection' and no extension method 'Connection' accepting a first argument of type 'DCApp' could be found (are you missing a using directive or an assembly reference?)

Error CS1061 'DCApp' does not contain a definition for 'Dispose' and no extension method 'Dispose' accepting a first argument of type 'DCApp' could be found (are you missing a using directive or an assembly reference?)

Error CS0103 The name 'Globale' does not exist in the current context

Error CS1061 'DCApp' does not contain a definition for 'CommandTimeout' and no extension method 'CommandTimeout' accepting a first argument of type 'DCApp' could be found (are you missing a using directive or an assembly reference?)