how to set an option for form->input( 'multiple'=>'checkbox')

i plan to set a checkbox with selected option in my form.
but i am unable to show my checkbox content in the form, i cant see any value instead of just a box for me to select.

how to show value while i using checkbox? i able to show my value while i using select.
this is in a HABTM model. any hints?

here is my selection code.

=> 'Select Related Potential',
//'options' => $users,




'selected' => $ownUserId, )); ?>