Yes, at the tail of each arrow, you have an actor with a certain Event name. In the case of Dispatchers and RoundRobins, you put this in the marked OutEvents label. At the head of each arrow, you have an actor whose Tag matches the Event at the tail.
So, to answer your question, you fill in the tags of the actors that you want the Dispatcher or RoundRobin to trigger.
Now, to clarify things, I'll give quick explanations of Dispatchers and RoundRobins.
A Dispatcher is a single actor that is used to trigger many things all in one action. You can also put time delays to make it wait a short time before triggering the next Event in its list, but you don't need to do that here. So, one of these Dispatchers will instantly trigger ALL of its events when something triggers it.
A RoundRobin has a set of events like a Dispatcher, but it works more like a switch. The first time you trigger a RoundRobin, it will trigger whatever OutEvents[0] matches. The second time, it will trigger OutEvents[1], and so on, until it gets to the end of its list. At that point, it will go back to the first event if bLoop=True, or it will shut down if bLoop=False.
So, here's an in-depth description of what this complex trigger machine does:
The player shoots either one of the Triggers, and it triggers a Dispatcher. That Dispatcher does two things: it triggers the RoundRobin, and it turns off the Trigger that was shot. This is so that the player can't just shoot the same Trigger twice to make the Mover work.
What does the RoundRobin do? Nothing, since we intentially left OutEvents[0] blank.
Then the player shoots the other Trigger, and something similar happens. That Trigger's Dispatcher triggers the RoundRobin and turns off the shot Trigger.
Now what does the RoundRobin do? Well, we made OutEvents[1] the tag of that last Dispatcher, so that's what becomes triggered next. That Dispatcher turns both original Triggers back on again, and then it triggers the Mover.
I hope I'm not bombarding you with too much information. I really am trying to be helpful.