How to communicate mathematics by computer and in the internet?

Question

I would like to know how can I exchange mathematical ideas with symbolic representations by computer, by e-mail or asking questions with formulas and mathematics symbols in the internet. For letters we have the keyboard but mathematics it is different due to the complexity. I have heard about Latex but I am not sure if it is the best solution for what I want... I also don`t understand very well what are macros and the difference between Tex e Latex.

For sure, LaTeX is the best way to do that. I suggest you to learn it.
And, of course, this is the place for asking questions and sharing mathematical ideas using $\LaTeX$.
To answer your last question: LaTeX is a language built on the language called TeX. In particular, the LaTeX compiler that I have interprets the code I have written, translates it to TeX, compiles it, and then gives me back the pdf. (I am pretty sure this is how it always works, but I am not 100% sure). You should not attempt to learn TeX before LaTeX; it's unnecessary and much less human-readable.
This is a helpful website if you don't know the $\LaTeX$ symbol for something: detexify.kirelabs.org/classify.html