Below are some free and pay resources that explain how to play pinball. All credit to original content creators.
I think for most people it will be helpful to watch the vids first. It can be tough to visualize the techniques when described in words.
Note: the videos and web pages will often use different names for the same technique but you'll learn what's what pretty quick. For example, some people call it a "bounce pass" while others call it a "dead flipper pass". Same technique.
Pinpin 7 - "Seven Flipper Skills You Need to Know". This is the second chapter in the film, about five minutes in. You can fast forward or sit through the opening pinball fishing video.
Short youtube video showing various flipper techniques:
(note: the "slingshot pass" technique shown (aka "post pass" or "post transfer") is not typically how this is done. The method shown in Pinpin 7 is how it is done on most games)
Pinball Techniques with Neil Shatz:
Short video showing some techniques. This is one of the few free videos that shows some multi-ball control techniques, however, it doesn't really explain how they're done.
This is a *long* (40 min) but well-made video. Though this is about Indy 500, if you are a novice it will convey the importance of having a game strategy to maximize points, extra balls, etc.
Pinball 101 DVD ($20): http://www.pinballvideo.com/
This was made by world champion Keith Elwin. If you just want one "all in one" package for learning pinball with good presentation and humor, this is it. In addition to what the free stuff above describes, pinball 101 additionally describes how to control multiple balls during multiball. You can google pinball 101 to find online retailers that sell it.
Pinball Basics ($15): http://home.myfairpoint.net/vze8f4tt/tomstwilightzonepinballmachineaccessories/id51.html
I haven't seen this one yet. Appears to cover similar material as pin 101 and I have seen generally favorable reviews from people who have it.
Pinball Rulesheets: http://pinball.org/
In-depth rule sheets for many popular games - because that little Rules card on the game just doesn't cut it for the more complicated games.
These are great articles with pictures from Martin Ayub, the editor of pinball news and one of the top players in the world.
Internet Pinball Database Guide: http://www.ipdb.org/playing/skills.html
Great info, but no pictures.
Three Rivers Pinball Guide (pdf): http://krellan.com/pinball/skillguide.pdf
This is an oldie but a goodie. It has some advice about how to handle the ball when it starts getting knocked around in the slingshots, as well as some tournament advice. Save a copy while you can as the hoster may take it down at any time.