Good question. I recommend reading the DAQmx Help and starting with the NI-DAQmx Key Concepts section. That will explain the different timing modes, trigger types, etc., and how they relate to the DAQmx API. I recommend reading your cDAQ chassis product manual (called User Guide and Specifications). It will break down the capabilities of your chassis in much more detail than the general DAQmx help.
The module user manuals aren't going to be much help to you learning the API. They largely list the specifications of the module when most of what you want is likely a feature of the chassis.
A good start is to read the sections in the help and chassis manual that interests you and then playing around with examples that use those features. If you want to see how the examples work but don't have hardware, you can go to MAX and simulate hardware to test.
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As for correlated and uncorrelated modules, I'm not sure what you mean. All cDAQ AO modules can be independently timed or share a sample clock with something else. We used to have a concept of correlated digital, where certain devices could not generate their own digital sample clock and you had to correlate it to another task, like analog input (see the cDAQ-9172 chassis). Again this is a feature of the chassis, not module.
There are many examples that use a trigger. Modifying them should be simple--just chose the terminal you want to use for your trigger. For an internal trigger you would chose an internal signal--like the start trigger from another task. For an external trigger just select a PFI line that you have it wired to, either on the chassis or a digital module.
I hope that helps.
