By default, only single rows can be selected, but you can allow multiple selection by setting the mode, like so:

refTreeSelection->set_mode(Gtk::SelectionMode::MULTIPLE);

For single-selection, you can just call get_selected(), like so:

auto iter = refTreeSelection->get_selected();
if(iter) //If anything is selected
{
  auto row = *iter;
  //Do something with the row.
}

For multiple-selection, you need to call get_selected_rows() or define a callback, and give it to selected_foreach(), selected_foreach_path(), or selected_foreach_iter(), like so:

refTreeSelection->selected_foreach_iter(
    sigc::mem_fun(*this, &TheClass::selected_row_callback) );

void TheClass::selected_row_callback(
    const Gtk::TreeModel::const_iterator& iter)
{
  auto row = *iter;
  //Do something with the row.
}

To respond to the user clicking on a row or range of rows, connect to the signal like so:

refTreeSelection->signal_changed().connect(
    sigc::mem_fun(*this, &Example_IconTheme::on_selection_changed)
);

Maybe the user should not be able to select every item in your list or tree. For instance, in the gtk-demo, you can select a demo to see the source code, but it doesn't make any sense to select a demo category.

To control which rows can be selected, use the set_select_function() method, providing a sigc::slot callback. For instance:

m_refTreeSelection->set_select_function( sigc::mem_fun(*this,
    &DemoWindow::select_function) );

and then

bool DemoWindow::select_function(
    const Glib::RefPtr<Gtk::TreeModel>& model,
    const Gtk::TreeModel::Path& path, bool)
{
  const auto iter = model->get_iter(path);
  return iter->children().empty(); // only allow leaf nodes to be selected
}

To change the selection, specify a Gtk::TreeModel::iterator or Gtk::TreeModel::Row, like so:

auto row = m_refModel->children()[5]; //The sixth row.
if(row)
  refTreeSelection->select(row.get_iter());

or

auto iter = m_refModel->children().begin()
if(iter)
  refTreeSelection->select(iter);