How can I open and close the tiny screws of my mobile phone if I don't have any type of tool to open that tiny screw? Suggest me the ways too by which I can make screwdrivers at home according to my need.
I have used a piece of adhesive tape in the past. You press it firmly against the head of the screw, then rotate the appropriate direction. To apply pressure more accurately it may help to press with a pencil eraser, the tip of a house key, or some other item with a small surface that is similar in size to the head of the screw.
The technique is NOT going to tighten a screw as well as a correctly-sized screwdriver, but it does work in a pinch.
I know some people might not open phones and computers as often as others, in my case opening devices is pretty much normal to me, so based on my experience; my answer to your first question is:
Don't try to substitute precision screwdrivers, there's no better tool for these type of screws than these precision screwdrivers, other objects for example a knife like it was suggested by another answer, will probably unscrew the screw, but there's a high possibility that it will damage the drive, damaging the drive will just make the task more tedious each time you try to disassemble your phone. Until you reach the point where you will simply not be able to screw or unscrew the screw. So my advice is to buy some precision screwdrivers, of course there are the expensive ones but you can also buy some for less than a dollar, and they will do the job just fine. It's better to do this the right way since I genuinely believe finding a substitute tool for a small screws it's going to be more damaging in the long run.
Again this is just my opinion
Depending on how small the screw groves are (and how thin the knife blade is), you may be able to use a knife tip to unscrew the screw. Just be careful not to break the knife.