About how many known elements are there on earth? are they all naturally made?

what are the main parts of an atom? where are they located within the atom?

There are exactly 92 elements on Earth, all products of nature.

More have been created in laboratory 'atom smashers' and
particle accelerators, but their atoms don't last long ... they fall apart.
(That's why these elements are not found in nature ... the Earth is
more than 4 billion years old, and those complicated atoms of
elements higher than #92 fell apart before now.)  

The main parts of the atom are:

-- the "nucleus", in the center, containing neutrons and protons;
   the number of protons is what determines what element it's an atom of

-- several electrons, whizzing around the nucleus, like planets in orbits,
but so fast that you can never know exactly where any electron is;  they
form kind a fuzzy cloud all around the nucleus;

-- the electrons are far away from the nucleus, so the atom is mostly
empty space;
I've read that if the cloud of whizzing electrons were the size of Texas,
then the nucleus in the center would be the size of a bunch of grapes ! 

--  most of the time, there are the same number of electrons as the
number of protons in the nucleus, but not always;
it's fairly easy for electrons to get pulled away from an atom atom, or to
temporarily hook up with an atom where it doesn't really belong;
one situation where this happens this happens is when there's an electric
current flowing in the substance ... a lot of electrons are drifting from one
atom to another, generally in the direction of the positive terminal of the battery.
For example:  If there's 1 Ampere of current flowing through a piece of wire,
then there are about  6,250,000,000,000,000,000 electrons flowing into
one end of the wire and out the other end, every second.