To write and edit LaTeX files, you can use any text editor such as Atom or Sublime Text but good LaTeX editors are available. Whatever tool you choose to use, you need a TeX distribution to build LaTeX files into an output such as PDF. You can download all this software for free.
Selecting a TeX Distribution
Before you can begin working with LaTeX, you need to first install a TeX distribution. This is a typesetting program that takes the LaTeX files and generates output based on the settings in the LaTeX files. TeX distributions are available for Linux, Windows and MAC.
For Windows, I recommend using MiKTeX which you can download at miktex.org/.
For MAC OS, you can use MacTeX, which can be downloaded at www.tug.org/mactex/.
Instructions for installing these programs are provided on the sites where they are available.
Selecting a LaTeX Editor
Using a simple text editor has its advantages. You can create LaTeX files in an editor such as NotePad++, Atom or Sublime Text. Nevertheless, plenty of good LaTeX editors are available.
For Windows, I use TeXworks which can be downloaded at www.tug.org/texworks/.
For MAC, a good tool is TeXnicCenter which can be downloaded at http://www.texniccenter.org/.
So, you can choose how you best want to work. For me, an editor that adds tags, closes tags correctly and has a menu selection for generating output works fine.