I searched from App Store, and found some of them. But if I will use, do they still take that large audiofile memory? As if I use a dictaphone on cell phone, the memory is not big for the voice recordings. But on Mac is vice versa.

The size of audio recordings depends on the file format. The standard is .wav files -- mp3 or mp4 files will be about 5x smaller, but have lower sound quality. DAWs [like GB] always record .wav files; I don't know what audio format will be recorded by dictaphone applications, you'd have to check the documentation for the application.

Wav is m4a? And mp3 takes less memory? On the dictaphone, what means bit rate, sample rate, 8000-48000 hz? As I have to choose between them. I want what takes less memory.

No, a .wav file is a [large] full-size full-quality WAV audiofile -- .mp4 or .m4a or .mp3 audiofiles are considerably smaller but somewhat lower-quality. Sample Rate and Bit Resolution / Bit Rate are measurements of the specs of a digital audio file -- those are complex digital theory concepts but if you wanted to learn about audio and digital theory you could watch the course linked above [click on the More Info box].

The mp3 takes the same amount of memory than QTP audio file. There are bit rate 64-320 kbps and sample rate 8000-48000 hz, do they effect to the size of file (less memory) if I choose the smallest number of them?

Yes, lower Sample Rates and lower Bitrates will result in smaller files, but also poorer sound quality. I'd leave the Sample Rate at the standard value (44.1k or 48k] and experiment with different Bitrates to see how small you can make the files before the loss of quality becomes unacceptable. However, audio file sizes are not that large compared with the capacity of modern hard drives, so unless you expect to accumulate a huge number of [lengthy] audio recordings I wouldn't worry about it too much -- after all you can always add another large hard drive.

Where to I can add another large hard drive, another internal one, or external one? What is an external hard drive, is it like a memory stick, just to keep datas.. ?

You can purchase an external hard drive from any place that sells computer accessories -- I prefer OWC : https://eshop.macsales.com/shop/external-storage#drive-configuration:single-bay https://eshop.macsales.com/shop/owc-mercury-elite-pro-mini/usb-c https://eshop.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB Note : - Mechanical hard drives [HDDs] are slower but less expensive per/GB; - SSDs [Solid State Drives] are faster but more expensive per/GB Make sure to choose an enclosure that includes the right connections to match the connections on your computer -- ideally that would be USB 3 with a USB 3.1connector or a USB C connector. The company's pre-sales tech support can help you select the right drive/model.