2. Define an entry point there:

using System;
using System.Collections.Generic;
using System.Text;
using Nevron.GraphicsCore;
using Nevron.Chart;
using Nevron.ReportingServices;

namespace SSRSCustomCode
{
    public class Class1
    {
        /// <summary>
  /// Main entry point
  /// </summary>
  /// <param name="context"></param>
  public static void RSMain(NRSChartCodeContext context)
  {
            // Do something here just like in SSRS
  }
    }
}
3. Call that entry from the SSRS designer:

using System;
using System.Drawing;
using Nevron.GraphicsCore;
using Nevron.Chart;
using Nevron.ReportingServices;
using SSRSCustomCode;

namespace MyNamespace
{
 /// <summary>
 /// Sample class
 /// </summary>
 public class MyClass
 {
  /// <summary>
  /// Main entry point
  /// </summary>
  /// <param name="context"></param>
  public static void RSMain(NRSChartCodeContext context)
  {
   Class1.RSMain(context);
  }
 }
}