Glib::RefPtr<Gtk::TreeSelection> refTreeSelection =
m_TreeView.get_selection();

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

refTreeSelection->set_mode(Gtk::SELECTION_MULTIPLE);

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

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

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

refTreeSelection->selected_foreach( 
    SigC::Slot(*this, &TheClass::selected_row_callback) );

...

void TheClass::selected_row_callback(const Gtk::TreeModel::iterator& iter)
{
  TreeModel::Row 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::slot(*this, &Example_StockBrowser::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::slot(*this, &DemoWindow::select_function) );

and then

bool DemoWindow::select_function(const Glib::RefPtr<Gtk::TreeModel>& model,
                                 const Gtk::TreeModel::Path& path, bool)
{
  const Gtk::TreeModel::iterator 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:

Gtk::TreeModel::Row row = m_refModel->children()[5]; //The fifth row.
if(row)
  refTreeSelection->select(row);

or

Gtk::TreeModel::iterator iter = m_refModel->children().begin()
if(iter)
  refTreeSelection->select(iter);