For uploading a file in cake php,you need to use type as file while generating the form.Along with this,add a field of Form with input type as file.
Example:
$this->Form->create('User',array('type'=>'file')); // equiv. to (enctype=multipart/form-data)
$this->Form->input('FILE',array('type'=>'file'));
Using this,you can easily your upload your file in cakePHP.