Here are some links you will find useful for learning LaTeX. You should use this page in conjunction with various pages in the Miscellaneous Advice link to Math 403, which is Geometry course I am teaching on line this term.
Sample LaTeX files from another course I sometimes teach. Download a file.tex to your desktop in the lab. Clicking on it should open the file in TeXShop. The (Typeset) button of TeXShop does what it says.
dbrisson's access texWins
Even if you don't have a LaTeX compiler installed on your current computer, you can still create a LaTeX file using texWins (again on any computer). All you need is a browser and a login. Unfortunately, I only have one login you can all share for the moment.
Of course, there is much more out there. Let me know when you find something worth sharing here. I'll add stuff in time too.