Dear @Mauro-A-Santos
the tools are very simple.
A good editor. Atom, Visual Studio or Sublime will do.
And FTP like Filezilla or Cyberduck are recommendable.
And off we go!
Github is not important to get started with.
I would watch 2 or 3 tutorials of how to build a Wordpress Theme from scratch. Maybe even a course at Udemy or Lynda.
If I work on Laytheme I just use Google Inspector, the CUSTOM CODE section and no tools.
Sometimes a code editor to backup the code which I wrote. But that is it.
Best!
Marius