Add new field to order and modify total_shipping

[Ilja Borisov]

Hi! In Presta 1.7.4.3 I want in carrier select step to add new hidden field. The idea is following: A client chooses pick point and its id or name goes to that field and then saves to new order field in database. So, I added a new field "carries_pick_point" in table "orders" and 

<input type="hidden" id="carrier_pick_point" name="carrier_pick_point" />

Where do I need to modify to make data from input save inside new field in DB? I gues in class Order.php, but dont know how to do it, please help.

The second problem is to modify delivery cost in the same step. I didnt find any input in that step, that stores delivery cost. How to modify total delivery cost in carrier step?