I have an F2, but just is case it's similar, here:
Originally Posted by pluto
There's a ring on each side "behind" the shoulder strap. The short ends of the FA-100 clip onto these. There's also a ring on each side in the back of the bag. The long ends of the FA-100 clip on to these. Once you get either of these pairs clipped it should be immediately clear how the rest of it goes.
Be aware, although the bag will then carry like a backpack it won't be one: Mind how you pack the pokey things. Your back will let you know if you've made a mistake. And, in the spirit of full disclosure, I've never used one.