In order to use LaTeX you need to install a few programs on your computer: The behind-the-scenes LaTeX compiler, and a front end that you actually see on the screen.

For a windows machine, first get the MiKTeX package and then the graphical front end TexMaker or TeXstudio
An alternative for windows: Download MiKTeX Portable and install it on your USB memory stick (about .5 GB required).

For mac os, the user interface TeXShop is very nice. Follow the instructions for BasicTex and TeXShop

To try LaTeX before you get your installation up and running, or if you don't have access to a machine on which you can install this software, you can use the web-based LaTeX environment Overleaf.

Help with the LaTeX commands can be found here. Here's a list of commands for producing math symbols.

Although the ubiquity of Adobe Acrobat reader has made the PDF file format a popular option, LaTeX documents have historically be typeset in the Adobe Postscript format. A powerful postscipt viewer program is GSView. To use it, you need to download both Ghostscript and GSView.