something like a summary of the most important facts.
There is no such thing. This program is so broad that "most important" will vary according to what use you want to make of it (web design, graphic design, photography, etc.)
where to find good free instruction for CS3 extended,
google. "photoshop cs3 extended tutorial [term]". no quotes. replace "[term]" with the feature you're interested in learning.
example "photoshop tutorial vanishing point"