How to build links in code using the ctools_modal_text_button() function?

How to build links in code using the ctools_modal_text_button() function?

On the Modal forms (with ctools) they say:
To build links in code I recommend using the ctools_modal_text_button()
function.
$links[] = ctools_modal_text_button(t('Modal Login'),
'modal_forms/nojs/login', t('Login via modal'));
$links[] = ctools_modal_text_button(t('Modal Login'),
'modal_forms/nojs/login', t('Login via modal'),
'ctools-modal-modal-popup-small');
Where should I enter this code? Witch file and after witch line?