I'd start with studying the history of diesel and it's progression from the first coal powered one all the way to the common rail we have now. That will give you more information on how they work. You can always back that up with more sources of information on theory of operation.
Then when you have a good grasp of the operation of a diesel and understand what the ECM would need to do to run an engine then open up a tune for the first generation LB7 Duramax and look over the tables. If you understand the diesel engine well enough the tables will make sense. Sure, don't expect to be able to understand each and every table. But you can search for the table number in this and other sites and read up on them.
Then when you get a good handle on the LB7, move to the LLY, then LBZ. Move your way up each generation of Duramax and you'll notice the additional tables and changes to the methods of controlling the fuel.
If you just want to tune your LB7 then you can stop at the LB7.
There are a handful of calculators such as the timing calculator, my defuel calculator and a few othere to help out.
Rule of thumb. Take it slow. Only make small changes to a single table at a time and see how it reacts.
There's not going to be anyone here or elsewhere that will hold your hand the whole way through the learning process. But we will be happy to help dig you how of a hole or assist you when you get stuck. But the learning part is all on you. As mentioned above, if you can get your hand on a Starlite book that would speed the process up considerably
