PPC is pay per click. You go to websites, like Google, and you set a price to have your advertisement (text or banner) listed. Every time someone clicks on your advertisement, it is deducted from the amount of money that you paid to have in your account. When your account balance is too low to afford another click, your advertisement stops being displayed.
Affiliate marketing is the process of having others (third parties) do your marketing for you. You may provide some marketing collateral (banners, text, etc.) but the third party is responsible for the marketing. They drive people to a specific webpage on your site that records both the sale information and the affiliate’s information. You then provide sale reports and commissions (5-50% or more) to the third party.
If you have time to do the marketing yourself, and can optimize your sales process, it’s probably less expensive to do PPC marketing through something like Google Adwords.
If you a) don’t have time for creating, monitoring and optimizing your own marketing campaign, b) want to build the power of tens or hundreds of third party sales people/companies, and c) have a product that allows you to pay higher commissions (digital products like software or ebooks), then affiliate marketing is definitely the way to go.
You can go look at
Commission Junction [not an affiliate link] to get an idea how to list your product and/or become a third party affiliate marketer. I believe you can set them up to be your third party distribution channel too. I’ve never used them, so please do your own research.