I recommend using the editor emacs.
If you're a Mac user then you can use TeXshop which is available here.
If you're a Linux (Redhat/Ubuntu/Debian/...) user then latex is probably on your computer already.
Some LaTeX info and tutorials
Here an introduction to LaTeX, thanks to Bin Zhang of SUNY, Stony Brook.
The Harvard TeX manual also provides a good introduction to TeX and LaTeX. This is useful for looking up commands.
Here's a reference for lots and lots of symbols.