There are basically two types of typesetting programs: Those that show the end product as you go; these are referred to as WYSIWYG, or "what you see is what you get". (If you've ever used MS Word, then you've enjoyed the simplicity of a WYSIWYG program.) The others are non-WYSIWYG, which usually means that it uses a markup language, like HTML does. A LaTeX file, like an HTML file, bears little resemblance to the displayed version of the file. In the HTML world, a browser is a program that takes in an HTML file and interprets it to form a webpage in the browser. Yes, there are WYSIWYG HTML authoring programs, but if you want, you can make an HTML file in a simple text editor, which in Windows is NotePad, which is what I usually use. Now, it's clear enough that my webpages are never going to win any awards for their beautiful design or layout, and that's fine by me, but when it comes to my typesetting mathematics, I want the best output I can afford. Oh, and by the way, there are free versions of LaTeX for all (or at least most) computer platforms.
By the way, if you have MS Word (recent version), you can can convert your Word document to an HTML document by just doing a SaveAs and then choosing the HTML format (extension).
Now for a quick history of LaTeX: it started with Plain TeX (by Donald Knuth) and was improved to today's version called LaTeX, which is a more user-friendly adaptation of Plain TeX. LaTeX was written by Leslie Lamport in 1984. It too has undergone many upgrades since then, and is currently available on most computer platforms (Windows, Macs, and Linux) for free. My own knowledge of it is these days on a Windows machine. It is easy to download for free and to install.
The original version of TeX (also called Plain TeX) was implemented and released to the public by mathematician Donald Knuth in 1978, with the intent of allowing anyone with a decent computer to produce beautiful mathematics into type. Nowadays, one can use either original TeX or LaTeX to produce beautiful output file in either DVI or PDF formats (the version I use produces PDF files). One rarely see DVI files anymore, and when my Windows computer encounters one, it somehow knows how make a screen graphic out of it and to print it to my printer, probably as a PDF file.
Today, the use of LaTeX is prominent among the major publishing houses which publish books/journals which contain a lot of mathematics. So, it's used not only for pure and applied mathematics, but also for writings in engineering, physics and the other sciences, though not so much in chemistry, but more about that in another section. One advantage of this publishing policy is that authors can write the LaTeX files themselves, retaining a lot of control over the final output form and saving the publisher a lot of time and money for them to typeset the work. One thing to remember, though, is that you can expect every publisher to have its own "in house" version of LaTeX style files (such as LaTeX2e, REVTeX, AmSTeX, AmSLaTeX, etc), though they may allow you to submit in any modern version of LaTeX.
I'm now going to state my rudimentary knowledge on how to download the installation files for LaTeX for a Windows machine. If you use some other platform, you should be able to do a search on the Internet to find the needed download and installation instructions.
So, for a Windows machine, like Windows 10, my trusted sources for these files are http://www.tug.org/ and https://miktex.org/download
1) I use the TeXworks version of a GUI for LaTeX: TeXworks-win-setup-.....exe executable (or something similar), which is currently about 24 MB.
2) I use the MiKTeX executable for the TeX engine itself: basic-miktex-21.6-x64.exe (or something similar) which is currently about 128 MB. (Install MiKTeX first, because it may be all you need.)
There are for-pay versions of LaTeX out there (at least there used to be) which build a useful GUI on top of the free TeX/LaTeX engine that runs underneath. However, the free version these days are so good the the pay versions may not be worth the price, but you'll have to check into that yourself. About twenty years ago, I had access to a Mac on which Textures by Blue Sky Research was available to me, but it seems as though that program has not been ported to the latest version of MacOS. Also, Overleaf (https://www.overleaf.com/) is an online LaTeX editor, which I have never used.
By the way, if you want to import graphics into your LaTeX documents, you might want to down load Inkscape, which is a free authoring program. I will deal more fully with the issue of generating graphics within TeX or importing a graphics file in more depth in another section.