The process for adding choices involves defining individual items and then printing them as a group:
Radio Buttons:
Add items: $form->addRadio($groupName, $label, $value);
Render group: $form->printRadioGroup($groupName, $label, $inline);
Checkboxes:
Add items: $form->addCheckbox($groupName, $label, $value);
Render group: $form->printCheckboxGroup($groupName, $label, $inline);