I am studying. = Ako ay nag-aaral.
I am studying/learning Tagalog. = Ako ay nag-aaral ng Tagalog.
I study everyday. = Ako ay nag-aaral araw-araw.
We do not really have the perfect tense pattern in Tagalog as it exists in English. We focus more on the time of the event, which relays to us the concept of the perfect tense.
I have been studying since last night. = Ako ay nag-aaral mula pa kagabi. (Can also be, "Ako ay kagabi pa nag-aaral.)
I have been studying Tagalog for a year now. = "Ako ay nag-aaral ng Tagalog nang may isang taon na." or "Ako ay may isang taon nang nag-aaral ng Tagalog." (For me, the second sentence feels more natural. Notice that in the first sentence, it ends with "na" = already. This "already" takes the place of "now".)
I have been studying Tagalog since I was a kid. = "Ako ay nag-aaral na ng Tagalog mula pa noong bata ako." (Notice the inclusion again of the "na" in this case. It's now meant to indicate that the study has been going on for a long time. The direct translation of the Tagalog sentence to English would be, "I have already been studying Tagalog since I was a kid." "...mula pa noong bata ako" can also be "mula noong bata pa ako.")
So, "have been studying" can simply be "nag-aaral", but the time reference can affect how the rest of the sentence would be.