I have started using Emacs as my editor after some years of using Vim. Well, I am enjoying it, and learning how to use it. One of the most important things to start with is the spell check. At least for me, this is a must-have feature.
First you need to be sure you have ispell or aspell installed.
sudo apt-get install ispell
sudo apt-get install aspell
If you are working on Mac OS X, you will need brew
brew install ispell
Once this package is installed, you just need to enable the spell check on the fly for GNU Emacs editor.
Where M-x is: Alt+x on Linux and press ESC then release and press x, on Mac OS X.
After that just type: flyspell-mode and hit enter.