: How does the Earth's gravity come about ?

: Is it due to the mass of the Earth itself ?

: If the Moon is as large as the Earth, will it has the same amount of gravity force as the Earth ?

: Why is it that we can't see a single thing in/on the black hole ? Does its gravity force works in the same way like the Earth (though its much much stronger) ?

: Hope these simple questions will not bother our pals here. Thanks !

All matter propagates gravity. The more matter there is the stronger the gravity. Why matter propagates gravity is a question that I dont think anyone yet knows.

Yes it the moon had the same mass as the earth, it would have the same gravitational pull as the earth.

The reason we can not see a black hole is that it absorbs all light that comes near it. Yes, this exactly the same as gravity on earth, only many many many times stronger.