Defensive/Offensive Forces

I have not gone to war before but I have been doing a lot of reading on this subject, and I've read conflicting information but as far as I understand it:

Defensive Forces are the Garrisons that protect objects such as cities, corps, bases, etc., and can NOT Attack the enemy. They can only hold position?

Offensive forces can Attack anything (including other Offensive) but cannot Garrison?

Do I have that right, and is that the ONLY difference?

i.e. (hypothetical situation):

if an Offensive army is in my country, I need another Offensive army to attack it??

Unless it attacks a city, where the Defensive army will defend the city,

but if it doesn't attack the city and I don't have an Offensive army, I cannot do anything about the enemy army?

if I have that right . . .

1) offensive forces DO attack garrisons. They will attack any target, defensive or offensive, providing you are using the right weapons against the right targets.

Defensive weapons, including garrisons, will defend when attacked, they do not initiate attacks. You would need offensive forces to initiate any attack on an enemy offensive force in your country, but should that offensive force of the enemy attack you, your defences will fight back.

The only sort of exception to this is stealth bombers which can attack random offensive units when their country is attacked or can be used to initiate attacks of any kind.

OK so I must say it's a bit more complex then it probably needs to be. It'd probably be easier for new people like myself to understand if they just merged Offensive and Defensive together, perhaps called "Military Forces," and allow the Military Forces to Garrison/defend/etc, as well as attack.