More specifically, how can I find this out using freebase? Turns out the steps you should take are:
Expand your query until you find the actor somewhere within the tree (keep on using
"*": null at each level down to get more detail)
Select the actor leaf in the query and use "Turn inside out" to arrange the query so that it will return actors constrained by film.
Repeat the above for the tv series
Combined the film and tv series constraints into one query.
Voila, you have all actors who appeared in Tron and Babylon 5.
You can easily extend this to do things like finding all Science Fiction films that anyone in Babylon 5 has starred in.
What you definitely shouldn't do is:
Find the MQL documentation
Wonder why you need to know so much about type theory
Now, that was a wasted hour. Honestly, just go straight to the Query Editor. You know it makes sense.