Making an app

Hi,

Maybe I will create a module up till now I am trying to figure out how to make an application with Drupal.

Does anyone know how to create a kind of a workflow. E.g user must visit content type screen X (display all items of a rental object) then press a button showing content types matching a criteria (show all available weeks with their prices) after the selection is made then the end week must be displayed
After that has done (one click only) the registration of the tenants must be entered (name, address, bank account).

So I have the following content types:
rental object (multi lingual)
weeks (date, weeknr, price, occupied, reserved). After a button is clicked all weeks after the current date with price and status must be displayed. After the click the weeks after the selected week must be displayed.
booking (main tenant, tenants). For the tenants only name and birthday. So content type booking is able to store 6 persons (max). For the main user the account, city etc. must be entered as well.

My main question is how do you create the flow in the app. Using buttons? Triggering things? How do you relate the content types with each other? Using hiddng fields? Code in PHP?
If I asking to much where is a good resource to learn things from. I have read a lot of stuf but I can't find these answers.

Thanks,
John

PS the current design (lacking a database) of the app can be find here http://members.chello.nl/jophof using Safari / Chrome