Alrighty, I'll try again.
Normally, I can do only a single action during an exchange. But I can choose to do a supplemental action as well at the cost of -1 to the roll. Not only that, but if I roll more than I needed to on my main action, the overflow rules (YS214) let me spend those 'extra' shifts to perform an additional supplemental action.
Example: I'm trying to run down a hallway, but there's a security guard blocking (in the way, not actually Blocking) my way. I start off by moving one zone to reach the security guard (a supplemental action). As my main action, I use ... oh, say a Fists maneuver to place a 'Flat on the floor' aspect on the guard. I roll, he resists, and I beat his roll with several shifts to spare (even counting the -1 for performing a supplemental move). The overflow rules allow me to spend those shifts to move additional zones, one zone per shift -- I've bowled over the guard, and continue running down the hallway. Summary: I've done two supplemental actions and a manuever action in a single exchange, without any stunts or powers to help me.
Are we on the same page so far?
Now lets add the Redirected Force stunt (YS152) to my character sheet and continue the ...
Example: Having made it past one guard, a second one charges at me and tries to tackle me. I easily beat his roll, which lets me trigger Redirected Force to knock him 'Flat on the floor', too. On the following exchange I can do nothing, while the security guard at my feet stands up and throws a punch, and the security guard I had left behind leaps to his feet and tries to catch up. Summary: I've done one maneuver action (a bit earlier than normal) as the entirety of what I'm allowed to do for the entire exchange, with no supplemental actions allowed.
If I had just let the attack miss instead of triggering the stunt, I could have reprised my last action, slamming the second guard against the wall and (assuming I rolled well enough, which I believe is likely do to the relative training levels) continuing down the hallway -- ie, maneuver plus overflow supplemental. If the optional Spin rules (YS214) were in effect, I might even have a +1 to my roll to do so, in effect increasing my sprint by an extra zone.
Was that any clearer?