Just like you can set a GtkCellRendererText editable, you can specify whether a GtkCellRendererToggle should change its state when clicked by setting the "activatable" property - either when you create the renderer (in which case all cells in that column will be clickable) or by connecting the renderer property to a model column of boolean type via attributes.
Connect to the "toggled" signal of the toggle cell renderer to be notified when the user clicks on a toggle button (or radio button). The user click will not change the value in the store, or the appearance of the value rendered. The toggle button will only change state when you update the value in the store. Until then it will be in an "inconsistent" state, which is also why you should read the current value of that cell from the model, and not from the cell renderer.
The callback for the "toggled" signal looks like this (the API reference is a bit lacking in this particular case):
void cell_toggled_callback (GtkCellRendererToggle *cell, gchar *path_string, gpointer user_data);
Just like with the "edited" signal of the text cell renderer, the tree path is passed to the "toggled" signal callback in string form. You can convert this into a GtkTreePath with gtk_tree_path_new_from_string, or convert it into an iter with gtk_tree_model_get_iter_from_string.