how to call to controller function when user selected a value in drop down list?

how can i create a drop down list with action which allow me link to other page?

i using cakephp to doing a system, which i wanna have a drop down list to let user select.
when user selected the value, i wanted to call a function in controller..
izit available that i can using a $form->input to perform this??

how can i call a function in a controller in this situation?
can i call a function while user selected a data and i send the data to controller??

any 1 can help? thanks..