I think, you are talking about Windows application.
You need to select the selectedItem of the listbox and get the Text from it.
Use the event, SelectedIndexChanged of Listbox.
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
int index;
index = listBox1.SelectedIndex;
string selectedText = string.Empty;
if (index >= 0)
{
selectedText = listBox1.GetItemText(listBox1.Items[index]).ToString();
}
}
Hope this helps.
cheers