Use the insert method to add items to the Listbox:
$lb->insert(index, element, element ... );
Each element is another line in the Listbox. The index is a valid index (see the sidebar "Listbox Indexes") before which the new elements will be inserted. For instance, to insert items at the end of the Listbox:
$lb->insert('end', @new_elements); # Or $lb->insert('end', "Item1", "Item2", "Item3");
To insert items at the beginning of the Listbox:
$lb->insert(0, @new_elements);