some IR sensor(ky-033) questions

hi,im new with arduino. i have a sketch by someone on youtube.

What i read from analog pin(A0) is either 800 or 17 with A2 as output HIGH

If i use 5v pin instead of A2,analog pin(A0) is either 750 or 65. im so confused why would it happen?

I measured the voltage between ky-033's v&g is 4.7 with A2 pin , 5.2V with 5v pin !

but it have same voltage 5.2v before connecting ky-033! why?

Really sorry for my bad english,hope you can understand what im trying to say!