How is the behavior graph event based?

DISCLAIMER: I don’t know if I’ve just misunderstood everything or if I don’t understand how it works or how it’s meant to work. I’m also not sure if this is the correct place to post this.

Can someone tell me how the UE4’s behavior graph is supposed to be event based? At the moment I can’t find any way other then using conditions to influence a behavior graph. When I hear EVENT based I think that when an event occurs a specific action should be taken. For example, let’s say you’ve got 3 different actions in a behavior graph. A patrol, follow and a stand part.

I thought this meant if event X occurred I could then tell the behavior graph to run the stand part.

But at the moment it seems like what I should do is if event X occurred I should then have conditions on those 3 parts and set the conditions on patrol and follow part to fail and set the condition on the stand part to succeed.

So it seems like those 3 parts should all be their own behavior graph and just have the behaviors be ran instead when an event occurs, is this how it should work? Am I understanding it correct now?

Just bumping this because I’m wondering the same too.
Also, do behaviour trees evaluate themselves constantly, or do I have to have a service at the root in order to evaluate it. Things like this are missing from the tutorial.