yeah, it could just be wording, but id recommend thinking of the routing in the way that the videos illustrate it… (both C&G and loopop do this excellently for Orac 2.0 ) as otherwise when you start creating more patches its going to get confusion.
the basic idea behind Orac is we have ‘module slots’ that can be filled with modules (like a synth,fx), this can be connected together in various configurations by a ‘router’.
the ‘default’ configuration, use by most is to configure have these modules organised in chains ( a bit like ‘tracks’ in a daw)
the reason this is done is because I wanted the flexibility of a ‘modular’ which allows swapping in/out of modules of functionality, but didn’t want the user to have to start ‘patching’ individual things together because this would be very tedious on these platforms which have very limited UI space.
(unlike a desktop/laptop where we have a nice big screen and mouse etc)
so by default what we have is:
S1 and S2 are ‘system module slots’, and usually left as they are. (router, clock)
S1 is usually the ‘parallel’ router module, is responsible for how messages are passed between modules - do NOT think of them flowing thru it, think of it as a controller.
(initially stick with parallel, as its usually more useful than serial)
S2 is usually the clock module
whilst starting out do not change this.
A1-A3, B1-B4,C1-3 are 10 module slots arranged into 3 chains, A,B and C
this is where you will normally place modules
chains are ‘configured’ in the router (S1) and this functionality includes audio in/out, mixing as well as midi in/out.
‘advanced’ module slots,
P1, pre- module … used for processing thing before they go to chains
P2, post-module… used for processing things after the chains
M1-M3 - modulation module slots, that are not connected to the audio, but are used for modulation module which can modulate parameters on other modules.
this may seem a little confusing at first, but as i said, all detailed in the various Orac 2.0 videos… and once you’ve seen it visualised it’s very straight forward.
the truth is… the above is all really use a ‘basic configuration’, under the covers Orac is much more flexible that the above might show…
really the heart of a Orac is an ‘engine’ that dynamically writes pure data patches - connect submodules together…advanced users could quite easily create their own ‘router’ module that have the module-slots configured in any number of different ways… and Orac could happily take this in its stride 
but… as of now, most find the ‘out of the box’ setup, flexible (intimidating ?!
) enough.