To address your points:
a) Gravity is present wherever mass is present. Every massive object is attracting every other massive object. The standard view is that mass has existed since the big bang; not something that evolved over substantial time. Mass accumulates to form stars and planets because of gravity. They could not exist without gravity. Gravity came before planets and stars.
b) Every substance on Earth, including you, contributes to the gravity of this planet. Adding more mass increases gravitational attraction. There is no chance or luck involved: gravity exists.
c) Adding mass increases the gravitational attraction exerted by a body. Removing mass decreases the attraction. Material falling to Earth changes Earth’s gravitation by a minuscule amount, as does loss of material like space probes or the outer atmosphere.
d) The gravitational field strength is not constant over the Earth. It varies with altitude and the presence of mass concentrations in the Earth for example.
e) In common logic the apple falls to Earth, but in reality the Earth also moves toward the apple. The force between them is identical… it just accelerates the much more massive Earth much less. It is all about mass and distance.
f) Mass causes gravity and applies to rocks, people, apples, balloons and clouds in the same way. The force applied by gravity can be opposed by other forces. In the case of a hot air balloon the opposition comes from the difference in air pressure between the top and bottom of the balloon (buoyancy). Aircraft do this with lift generated by wings. An object dropped on Earth falls toward the Earth because it is most strongly attracted in that direction. An object dropped on the Moon (yes the experiment was done) falls toward the Moon for the same reason. The Moon falls toward the Earth (orbit) because the attraction of the earth is stronger than the attraction of the Sun… but the attraction to the Sun is there. Objects placed about 1.5 million kilometres toward the Sun experience roughly equal attraction to the Sun and Earth and tend to stay there (its actually slightly more complicated than that).

a) What causes gravity to be created in this universe/earth? The theory of gravity has been used to explain the work of the support of the universe in order to enable the universe to maintain its operation. What causes gravity to be created since beginning? If the world is formed through evolution, how could gravity come about through the creation of earth/universe?

b) What substance to cause gravity to exist on earth? Is it by chance or by luck? What factors that cause gravity to exist permanently on earth/universe?

c) Would gravity be reduced or increased by external factors/influence?

d) If gravity on earth has to maintained at certain rate or number, what factors that cause the gravity to be stagnant and unchangeable?

e) As apples are always dropped to the earth, the gravity should be from the earth that causes apples to drop. What factors that come from the earth that contributes gravity that causes substance to drop?

f) As apples are always dropped to the earth, the air, cloud, sky and etc. do not seem to have gravity, why is it that gravity is always directed from earth and not elsewhere? What causes it then?