Difference between Tracking Specification and Reservation

Hi all,

I want to understand the exact difference between the Tracking Specification table and the Reservation entry table. The root of my problem stems from that I automatically create sales and purchase orders on another company (I do not use intercompany facility because creation of those orders requires extra business logic which intercompany is unable to provide). I can neatly create necessary sales lines and purchase lines but the problem pop-ups when the lines have items which requires item tracking (items were made company-independent). What my customer expects is to post those created orders with merely pushing the F11 button. I just try to make some educated guess about the workings of those two tables but I saw that I am not educated enough .
Tracking the code that handles item tracking adds extra confusion to my chore.