How to use the assault pack with the ruck sack

I am a civilian, retired from the Air Force. Never officially carried a ruck sack besides our shitty one week field exercise where we slept in AC tents lol sorry Army love you guys mean it. Even then we had basic issued backpacks that weren't even like official rucks. Anyway my question is I have two assault packs one for my SHTF stuff the other is an everyday day bag. I got a rucksack with frame Medium from a local surplus store and I saw the ruck and assault can connect to each other. My question is do you load the assault pack and the ruck and connect them or do you load the ruck and leave the assault mostly empty connected? I appreciate your answers and please understand yes I'm dumb, I was not army, never did any long rucks etc. we were never taught how to prepare for these things.