2) Four fundamental forces: Gravitation

Gravity or gravitation is one of four fundamental forces in the universe. It is also the weakest one as I said in the last post. Unlike other forces it works on much bigger distances. And it only pushes things together.
Imagine having a planet like Earth. It has poles. South pole and north pole. We can see that Earth gravity is pretty strong, it holds us here. So if electromagnetic force is 10^40(something like that) stronger, shouldn´t be electromagnetic field of earth insanely strong? No because electromagnetism works with +(plus) and -(minus) and they will cancel out (almost). Strong and weak interaction are working only on short distances so when you are forming galaxy or star you will work only with gravity.

There are two ways of imagining gravity. (Actually there are more but those are basic)
1) Newton´s way
It says something like this: Every particle in universe attracts all other particles in universe by force which is higher when mass of particles is bigger and is lower when particles are far away each other. Its equation is F=G*(m1*m2)/r
F is force of gravity
G is gravity constant (you can find it on wikipedia)
m1,m2 are masses of your objects
r is distance of objects
2)Einstein´s way

Spacetime is bended by all particles with mass. And it works with all particles even those which are massless, like photons.
Newton´s way does not actually explain some things like orbital of Mars (so it is kind of broken).
On the left is picture of spacetime. You can also imagine your bed which is probably very soft and when you push your matress it goes down. At that point your fist is actually kind of planet, star or black hole and it atracts other stuff around. If you take a ball lay it next to your hand it will go down to center of that hole you created.
I have found awesome video on gravity so here is link: https://www.youtube.com/watch?v=MTY1Kje0yLg
You will see that all forces have some force carrier. Gravitational carrier is massless particle called graviton. It is theoretical, which means it was not detected. Scientists even think that it cannot be detected, but we can see what it does: Gravity!