What is the difference between a trigger and a swap set?

Triggers can be used to trigger replays, cycle layers, and other things. But when talking about triggers and swapsets, adding a trigger to a layer in the artwork hides the layer until triggered. The trigger makes that layer visible. So if you want exclamation marks to appear when the character is confused, you could use a trigger. Its normally hidden, but pressing a key makes it appear.

A swap set is a group of triggers where exactly one trigger is active at a time. If one trigger in the set is turned on, all others in the set are turned off. E.g. if you have 5 hand positions or several eye brow positions for different emtions etc, you can put a trigger on each layer then add them all to a swapset. One of the set will always be on and the rest off. A swap set has a "default" trigger that will be on by default, until one of the other triggers is used. So you often have a "left hand swap set", a "right hand swapset", you might have a "eyebrows" swap set. etc.

Note: Head Turner is kinda like a swapset. It automatically turns on a profile and disables the others.

Also note that the layer being triggered can have behaviors in it. E.g. i might have a happy mouth and a sad mouth with a different set of visemes. There should ALWAYs be a mouth displayed, so I use a swap set. It guarantees there is always exactly one mouth displayed. I also use it sometimes for sets of eyes etc. for emotions.