One thing that isn't illustrated in this example is the actual mapping of variables to values in the container. In this instance, since there was only one variable (SourceFileName), and only value per loop to which that variable could map, that SSIS was able to map the two automatically.

But what happens (or, possibly better phrased), what does it look like when I have multiple values and variables? How do I map Var1 to Val1 and Var2 to Val2?