Iv noticed that ALOT of videos on youtube, when people are playing they have a earphone in one ear, i mean, why ? You can clearly hear that the backing track is going out of a laptop/stereo system, and the guitar is comin from the amp(???), so why put it earphones, this is what i dont get, what is this trickery
What is this recording method ? Maybe I overlook something
They're likely listening to the track while playing along and their mic is recording their room/amp and then they went and sync'd up the song when they were editing the video.
It's a trick of production. They will feed a click or backing track to their headphones while also recording the separate device, (be it guitar, bass, vocals).....but in the end they can mix it all.

while recording they hear a click track or whatever, but at the end, the final result is a combo of anything they want.

For my youtube hosted drum covers, I'll play the song in the background of my headphones and a loud click track but in the final result, the audience hears a very fine mix which sounds like I have found a magical Drum-less version of the song....LOL
But iv tryed that and having one ear for playing and one ear to focus on the track is somewhat bothersome. For me it kinda 'messes' up things
Well...you could use an audio interface to make a mix of what you want for your headphones while setting whatever inputs you want to record. Then sync up the playback files you want with what you recorded. I will play out of both L and R channels of the headphones.
To monitor things. With my band when we record I'm the drummer and a lot of my fills are triggered via vocal q's so I have to have headphones with extra vocals in them so I can clearly hear our singer.