Here is the simplified code of my program. Help sort out, newcomer. Thank you so much!

class program
  {
    Public struct dttable
    {
      Float Cash;
      int quancar1;
      DTTable Calc ()
      {
        DTTable MYTable = New Dttable ();
        int quancar1 = 0
            quancar1 = quancar1 + 10;
        }
        Return (MYTABLE);
      }
      Public Void SetDatatable (Dttable Indata)
      {
        Console.WriteLine ("Total: {0}", quancar1);
      }
      Static Void Main (String [] Args)
      {
        SETDATATABLE (CALC ()); // Error here
      }
    }
  }

Answer 1, Authority 100%

Make the setDatatable static method (write at the beginning of the STATIC modifier) ​​- and you will be happy.

Judging by the question, you do not understand what an object is, reference type and static class member.
Read the basics.
You can see a small lesson or some other, but be sure to deal with what is Object.