PPC stands for "pay per click", and is an advertising model upon which much of the internet relies on for its revenue.
In simple terms, webmasters usually designate a space on their website on which they're happy to allocate to ads - and then an ad server will decide which ads to show in that placement based on which advertisers are willing to bid for that space, and how much they are willing to pay for each click - sort of like an auction.
Ad space up for grabs can be found almost everywhere: On Google search results pages through to blogs, YouTube or pretty much any type of website...
Getting started with PPC
Google is by far the largest player in the ppc game, so I'd recommend beginning with the Google AdWords study material.
This will help you get a pretty comprehensive view of how to run campaigns, how advertising works.
Google have recently launched a program called "Google Partners", so I think that's a great place to start: http://gcptransition.appspot.com/
Twitter is a good place to start, and I particularly enjoy the PPC news and content published by PPC Hero.
