Hi,
I admit when I first started I just examined lots of page codes to understand how to add and edit articles. Much later I've founded the a good source which I'd like to share:
http://en.wikipedia.org/wiki/Help:Wiki_markup general
http://en.wikipedia.org/wiki/Wikipedia:PIC picture tutorial
http://en.wikipedia.org/wiki/Help:Table for structured tables
http://en.wikipedia.org/wiki/Help:Template for templates
I hope these help whomever needs them :)