how make bill in datagridview

Not sure of if you are talking of Windows app or Web app.

In either case, you need to traverse row-wise data present in grid. get the column values and add them up.

Ex in web:

//Something similar to this
int total = 0;
protected void DataGrid_ItemDataBound(object sender, DataGridItemEventArgs e)
{
     Textbox tbx = (TextBox)e.Row.FindControl("column2textbox");
     if (tbx != null)
     {
         // you got tbx.Text  value here. Do any calculation desired.
         // total += Convert.ToInt32(tbx.Text) ;
     }
}
// After DataBind() event of grid, use this total value to show anywhere.