I’m not recording on my cellphone alone, because I can’t rely on the quality (I don’t know if it’s my case, but please tell me if Samsung S6 is great enough to record audio), therefore I decided to use external microphone.
I don’t know, but the mic built into most cell phones is pretty good. Except (like your lavalier mic), they are not directional which means they pick-up background noise from all-around in addition to the sound you want to record, and they can be overloaded and distort if you try to record a rock band or something like that.
If you want to record directly from your phone, you might want to get a mic-stand holder/adapter (and a microphone stand) to get a good microphone-position while avoid handling noise.
The mic built-into a laptop is usually pretty good too but it will pick-up fan & hard drive noise and clicking from the keyboard, etc., so a phone often works much better.
I tried googling for Audacity tutorial, nothings helps, neither Treble or Bass or Equalization or anything I’ve found online to improve the quality of my sound recording.
I like to start with the philosophy that a good recording doesn’t need any effects or processing (except for level adjustment). …That’s just an ideal and it’s not always practical, and in the real world almost all professional recordings do have some compression and equalization, but it all starts with a good-clean recoding.
…I know you have a limited budget, but just as a point-of-reference, “good” stage/studio microphones don’t work directly with a computer or phone, so don’t waste too much money on a “computer mic”. Computer mics use an unbalanced (2-wire) connection with 5V supplied by the soundcard for electret condenser mics.
Stage/studio microphones are low-impedance balanced (3-wire) and studio condenser mics need 48V phantom power. (48V Phantom power is supplied by the audio interface, preamp, or mixer.) Dynamic mics (such as the famous Shure SM57/58) don’t require power, but they do have balanced connections so they don’t work “properly” with a laptop or regular soundcard.
Most people doing voice-over work or making audiobooks in a “home studio” use a directional [u]Studio Condenser Microphone[/u] (usually $100 USD or more) and a [u]USB Audio Interface[/u] with “proper” microphone inputs (also usually $100 or more). Or you can get a “studio style” [u]USB microphone[/u] (AKA a “podcast mic”). USB mics are easy to use and they don’t necessarily cost more than a good-quality analog mic. Some of them have a headphone jack or other features.
Another option (in a similar price range) is a portable [u]Solid State Recorder[/u]. These things usually come with good built-in mics and most can record in stereo.
A couple hundred (or a few-hundred) dollars may seem like a lot, but the computer is still the most expensive part and in the “analog days” it would have cost as much as a new car to set-up a home studio, and the quality wouldn’t be as good as a modern digital setup.
And that brings-up “the studio”… If you want nearly-professional results you need a good-quiet, sound-absorbing “studio”. And that can get very expensive! There are some “tricks”, such as recording at the right time of day, and turning-off the heating & air conditioning and any appliances that make noise, hanging blankets or other sound-absorbing materials, etc., and depending on the environment you start with, you may get acceptable results without spending lot of money.
….The soundproof studio is the biggest difference between a professional recording studio and a low-to-medium quality home studio. It doesn’t take super-expensive equipment to get a professional-quality recording but it does require a quiet environment.