Get value of text input in module

[pl.sabotinov]

I have made a custom form in my module template where customers input some text data. So after the submit i am able to get the data in Cart.php (for example) by the function Tools::getValue('name of input field'). Also i have made another attepmt and modified one ot the core tpl files. Added one input text field in core form and also i can get the value of this input field in Cart.php file. 

But the problem is i can not get this value inside my module php file. How or where should i use Tools::getValue in my module to be able to get the value? I have several registered hooks, but seems they are executed before form is submitted or i am doing something wrong and can not get the value inside my module to make DB insert. Or i should use(register) some other hook - like actionOrderConfirmation... to get the value after the form submitting. Whould you help me to do it correctly.