PPC is an acronym for Pay-Per-Click.  PPC programs are basically areas in the Search Engines where you bid for placement. 

How does it work?
You research your competitors, find out what they are bidding on and how much they are bidding.  Then you compete against them by trying to out-bid them for higher placement in the Search Engine.  Placement with PPC is dependent upon your budget and the how fierce the competition.  To reduce the expense you can target your local area paying only for traffic from the targeted area. 

Why use PPC?
The answer to that question for a brand new website is simple - immediate high-ranking placement in a search engine.  Sites can reach top status within 12 hours of launching a PPC program.  For a website that's been around a while, PPC marketing is a dynamic tool in your marketing arsenol. If you are going to budget marketing dollars for your business or website, PPC marketing ensures that your website link is seen. It's much like investing in a billboard on the side of a major interstate. PPC marketing ensures you will be seen. PPC marketing does not guarantee that those who see you will become traffic to your site, but it does ensure you will be seen. 

Where do I find PPC ads?
The most common place to find a PPC ad is at the top of a search engine. For example, on http://www.google.com/, the PPC area is at the top of the index in a blue bar and down the right side of the page. They are typically labeled as Sponsored Links.  Another place you might have seen PPC’s is on a web page, usually at the bottom, in an area called Advertisement Links or Sponsored Links or Google Ads? These are PPC ads. That website is pulling in PPC ads that are relevant to the content of that page providing you with links to similar content. That type of marketing is known as Content Targeting or Target Marketing.  

If I've done SEO properly, do I need to do PPC marketing?
That depends on how new your website is and how much traffic you want on your site.  If you have a new website, SEO alone will not get you placement for a while. SEO will ensure that your chances are higher for placement sometime in the next 2-6 weeks. PPC will ensure that you get immediate placement. Typically speaking, if you combine the two together, you will notice a significant decrease over time in the money you are paying out for PPC marketing because your site will rise in the actual search engine (index) lessening the need to for PPC traffic.