Intersect or except queries

[marcosql]

I've just posted a more specific question about the equivalent of EXCEPT clause for mysql, but I would like to get help on the right keywords to search for in order to learn how to perform intersection and exception queries in mysql. I want to find the information myself and not clutter the forum with too basic questions, but the keywords I'm searching for don't seem to return results that apply in MySQL. I need to find information on:

How to 'substract' records from a larger found set (EXCEPT)
How to work with intersections across joined or left joined tables
etc.

Thanks a lot, sorry for being to basic. My knowledge is growing every day.

Marco