EL is used to quickly access bean properties, Array and Collection contents. Also for mathematic operations and conditional checks.
On it's most complex level you can even create EL functions.
It's syntax is also 'eye-friendly' for non-developers.
You can also use EL in conjunction with JSTL, the most common way is using a runtime expression.
This code demonstrates:
As for the tutorial, check here:
http://java.sun.com/j2ee/1.4/docs/tutorial/doc/JSPIntro7.html