You have to specify the location
Label l = new Label();
l.Text = "Hello1";
l.Location = new Point(0, 0);
Label ll = new Label();
ll.Text = "Hello2";
l.Location = new Point(0, 20);
ll.Margin = new Padding(50, 50, 0, 0);
ShowAllItemContainer.Controls.Add(l);
ShowAllItemContainer.Controls.Add(ll);
Also you can achieve it using flowlayout panel
Label l = new Label();
l.Text = "Hello1";
Label ll = new Label();
ll.Text = "Hello2";
flowLayoutPanel1.Controls.Add(l);
flowLayoutPanel1.Controls.Add(ll);
flowLayoutPanel1.FlowDirection = FlowDirection.TopDown;