One, the Numbers documentation could do a better job on this topic. What I've learned is trial and error.
Two, Numbers could do a better job of being more explicit in its naming.
Having said that, I have to admit I like how it works.
Let's say in Column A, you've got a column of months ... Jan to Dec.
In Column B you've got data, at the bottom of your data you want first quarter results ... All you need to type is =Jan+Feb+Mar. Numbers recognizes where the data comes from.
You don't need to explicitly name the cells "Jan" etc. it knows. it appears to be case sensitive. It doesn't recognize "Mar" as "mar".
This works pretty well in a table format. Maybe not so good if you're not.
mt