Do I need to devise ways to access the data in the SD card on Android?

I just started studying Android the other day, and the theory is
I don't understand it at all yet, so I would like you to give me guidance based on precautions.

Refer to the site, etc., until
Press the button to play mp3 in the resource. It's done.

And now I'm looking for a site to access the data in my SD card.
There are many pages that say, "It depends on the model, so you need to devise it." In fact, how
I don't know if I should get it.

http://nobuo-create.net/sdcard-2/
http://techbooster.org/android/application/16004/

I used the above site as a reference, but the year of renewal is old as 2012, 2013 and
I don't know if the situation is still the same now.

I'm Android Studio 2.2.1, probably the latest environment, but even with the current version
Allowing the emulator to recognize the SD is also a direct
directly using /system/etc/vold.fstab. Do I have to edit it?

Also, after actual recognition, the site's sample source,
『//
Steps similar to "Methods to Get SD Card Mounted" Do I still have to step on it?

To sum up, here are the following points.
1. Latest way to get emulator to recognize SD card in Android Studio 2.2.1
2.How to retrieve MP3 files in SD card

I'd like to know how to do these, but if you could give me a sample that works up to here,
br/> Thank you very much.

Thank you for your cooperation.