I'm trying to learn all this, I have the same issue. So far my best interpretation is that order means energy-transfering organization, a solid is ordered, a gaz is not. It's not to be seen as complex vs simple, a machine is more complex than a bunch of cold molecules, but it's would be less chaotic in that sense.

Another definition is the number of possible microstates that can be reached. A cold universe of evenly distributed particles would be the upper limit of these microstates.

ps: coursera just started this https://www.coursera.org/learn/statistical-thermodynamics