I recently bought a cheap Samick Les Paul-like guitar. I found that the strings are too distant from the fretboard. Can it affect my playing, tone and whatnot? One more thing, I also found that the fretboard is too flat, almost like a acoustic guitar. Is it a problem or it's just normal? Sorry if my questions sound dumb. I'm a newbie after all.

the strings being too distant from the fretboard is nothing wrong, only depends on you whether or not you're comfortable with playing it that high though most people prefer it close to the fretboard because it's easier to play that way.

the fretboard being flat is notmal too.

Thanks for the reply, anyway i found that my guitar (Samick AV1) has an adjustable bridge. Does it mean that I can adjust the string distance to be closer to the fretboard? How can I do it? Is there any specific method to do so?

adjustable bridge? you mean a floating bridge? got whammy bar ar? a stick sticking out of the bridge?

My guitar doesn't have whammy bar. I think it has a Tune-O-Matic bridge.

I found that the strings are too distant from the fretboard. - > This adjustment is called "action".
Can it affect my playing, tone and whatnot? - > Playing yes, tone no. Shredding requires low action, and slide guitar requires high action.
I also found that the fretboard is too flat, almost like a acoustic guitar. Is it a problem or it's just normal? - > It's not a problem, it's just cheap. A radiused fretboard facilitates string bending and contributes to overall playability.
anyway i found that my guitar (Samick AV1) has an adjustable bridge. Does it mean that I can adjust the string distance to be closer to the fretboard? -> Yes.
How can I do it? Is there any specific method to do so? - > Yes. Take it to a pro. Let's just say that there's possibility your neck will have to be adjusted also. And let's just say cheap guitars generally don't respond well to adjustments.

Hmm.. maybe different guitar company prefer different fingerboard profile??? I have Ibanez RGT42 (with WizardII neck) and for me the fingerboard seems rather flat compared to my other guitar, a cheapo Aria Pro II which has curve and inclined fingerboard. ... Or... maybe the RGT is just another cheap guitar

But in your case, the RG is supposed to be flatter.
BTW, your guitar is still cheap.

Unless you want to have whammy bar effects, screw the damn floating bridge down (simply open up the back and increase the tension on the springs). Then decrease the action (action is the distance of strings to the fretboard) till you can play it without he strings vibrating against the frets that you're not playing, for example, when you play the third fret, make sure that the string does not touch the 4th fret in any way.

Finally, adjust the string length to such a way that the 12th fret natural harmonic is the same as a fretted 12th note.

Once that's done, have fun shredding away!

TS' guitar does not have whammy bar