Another note on the level of systems knowledge DAL expects you to have:

Gone are the days of being able to build the airplane from rivet #1 through the final fuel line and electrical connections. They expect you to continually increase your systems knowledge while on line, though, as a function of being a proficient, professional pilot.

They don't expect you to diagram the fuel, electrical and hydraulic systems during your training/checkride. If you study the LOD (as stated above) and the cbt (computer based training) you will have a good 'operational knowledge' to pass your systems validation and enter the sim.

From there, the training focuses on the ideas of 'what's going on with my ship' and, if it's non-normal, where do I go to deal with that abnormality. Along the way, you are taught how DAL flies the airplane and all the SOPs that go along with line flying. tweetfaip said it well in the summary of 'putting it all together' in the sim.