Hi, here I am going to fill my combo box "
cmbCategory" with 
dictionary "_dtcCategory". Its pretty simple
Here is the Code:
       Dictionary < int, string > _dtcCategory = new Dictionary < int, string > ();
       _dtcCategory.Add(0, "       -Select-      ");
       _dtcCategory.Add(1, "Students");
       _dtcCategory.Add(2, "Employees");
       cmbCategory.DataSource = new BindingSource(_dtcCategory, null);
       cmbCategory.DisplayMember = "Value";
       cmbCategory.ValueMember = "Key";