Yep, A1 is the final output if you have only one output port on your system.

In this scenario you may want to visit the Options - Preferences - Audio Tab and check the box for
'Unassigned output ports work as Subgroups' option.

Then you'll only see 'A1' in that area of the mixer and the rest become 'G' something (numerical numbering). This is a way to send desired tracks to a 'subgroup' that is inserted inline if additional audio output ports aren't needed or available.
This means any track that is routing to a 'Subgroup' goes to that 'G' channel strip before eventually being sent to the A1 output.
This gives the option of having subgroups you can control (ie point all drum tracks to subgroup 3 and gain the ability to turn all drum tracks up/down uniformly, or all guitars etc)
This is what I consider an Advanced User feature, so it may be beyond your need right now, but wanted to point it out.

But anyway, from your description, yes A1 is the final output in RB before being sent out and to the soundcard/interface or other software, since you only have 1 output port available.

Make your sound your own!
.. I do not work here, but the benefits are still awesome