How would I add actors to a list?

So I can use a script to display a random actor from a list?

The list blocks are under Attributes > Lists.  To get a random actor from that list, use the "random number between __ and __" block with the "get item # __ from __" block.

To add an actor to the list, you will need to use the "add _ to list _" block with the "actortype" block in the Actor->Properties palette (unless you really mean "actor", which would be in the Scene->Actors palette).