If the speaker said it correctly, what was said was, "Kailangan ko muna ang mag-aral." = I need/have to study first. When we say that sentence, usually the "muna ang" comes out as "munang" and it's very possible that some listeners would miss the "ng" sound at the end of it, thus getting the impression that what was said was just "muna". However, if you'd rephrase the sentence, it will come out correctly as "ANG mag-aral muna ang kailangan ko." and not "Mag-aral muna ang kailangan ko." Aside from Green's explanation of "aral-aralan", it may be possible also that the word is "aral-aralin", which means to study something at leisure and also not necessarily in-depth. Similarly, when we say "basa-basahin ang libro", we mean to browse the book and not read it cover to cover.

The correct way to write it is: Kailangan ko muna mag-aral. Aral-aralan. Which means, I have to study first. Pretend to study/ to be studying. Remember that each time a noun (in its base form) is reduplicated followed by the suffix "-an", it implies pretense or diminution of what the word truly mean. For example, bahay(house) - bahay-bahayan(play house); bundok(mountain) - bundok-bundukan(hill,mound,or just some pile of earth); tulog(sleep,n.)- tulog-tulogan (pretend to be asleep); it's also applicable to any noun even with proper ones, like Einstein-einsteinan (pretending/acting like Einsten. :)

The first sentence means He/She needs to study. Kelangan or Kailangan (Need) Ko ( I ) Mag aral ( Study) And for the second word "Aral- Aralan" sounds funny because for me it is like saying that He/She needs to study but he truth is not. Hope you understand..:)