Application Express :: Replacing Insert And Update Button Processes

Getting starting with diving deeper into APEX and reading the developers guide all 800 pages of it! Thing is I'd like to get started with some of the more interesting stuff.

I have created a form page based on the "Form on a Table with Report". The report part looks fine. What I'd like to do now is use an API I've built to change how the insert and update works. So when the submit button is pressed it rather performs an API call to the procedure/function.

1. Should the API be a function or procedure. In my playing around I saw that a procedure might work better or easier to implement
2. How would I go about creating a call for the button to use instead of the current processes?

----------------------------
Apex 4.2
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
Linux version 2.6.32-279.19.1.el6.i686
----------------------------