Actor events are done kind of like triggers are but more compact. There is an event portion, events can be anything that can happen to the actor itself and a few other things (abilities, behaviours, events and others). I am still not sure what they all do/are used for. Now when the event happens the action portion is done (Note: you can only have 1 event and 1 action per event). The action portion are manipulations on the actor for the most part (there are also other things like setting references). They are mostly used for setting actor properties and playing animations (although as you can probably see there are lots of others).
The last piece is the terms. Terms modify the event or action. You can have multiple terms in an event. Terms can act like if statements where the term needs to be fulfilled to have the action happen (validator terms) or they can do things like change where the action takes place (the At term). There are probably other things that they do that I have yet to see but those are the ones I have worked with. (Note: You can have as many terms in an event as you wish)