How To Access Form Element In Controller

How can I access the elements of my view in controller. lets I have a field name 'type' in my form field and I want to access the value of that field in my controller class. How can I achieve that. I saw where we are fetching all attributes

$model->attributes=$_POST['Alerts'];
How can I get a specific attribute from $model->attributes Thanks in advance

I want to pass a value from form to the model.