ながら = whilst, designates the adverb which modified the verb.
I guess when you say "main action", that would be the main verb at the end of the sentence. But that is just a guess. You simply have to figure out the "whilst" part.
E.g. Is it:
1. I work part time whilst at university.
(I don't know how to write this one using ながら)
or
2. I study whilst working part time.
アルバイをしながら大学に行きます。
I don't know what's on your test paper, but you need to do the rest by yourself, otherwise you won't get through the test.