Writing in LaTeX

Essentially all math is written with a program called LaTeX. You can download a LaTeX program to your computer (eg., TeXworks), or you can write it online through a website like Overleaf.com

In fact, Overleaf has a great page which introduces you to LaTeX. Here it is: 

Almost all math is written with a program called LaTeX. You can type in LaTeX by downloading a LaTeX editor to your computer (eg., TeXworks), or by using a website which hosts a cloud-based editor (eg., Overleaf).

In fact, Overleaf has a page called "Learn LaTeX in 30 minutes" which you can check out here.