You whack the subitems into an array and add the array as a list item.
The order in which you add values to the array dictates the column they appear under so think of your sub item headings as [0],[1],[2] etc.
Here’s a code sample:
//In this example an array of three items is added to a three column listview
string[] saLvwItem = new string[3];
foreach (string wholeitem in listofitems)
{
saLvwItem[0] = "Status Message";
saLvwItem[1] = wholeitem;
saLvwItem[2] = DateTime.Now.ToString("dddd dd/MM/yyyy - HH:mm:ss");
ListViewItem lvi = new ListViewItem(saLvwItem);
lvwMyListView.Items.Add(lvi);
}