PPC or Pay Per Click is exactly what it says.
You pay per each click that comes to your website. You will bid on a certain keyword (e.g. "Download TV Shows") - so when someone searches for that keyword, your ad will show up.
PPC campaigns are a brilliant way to send paid traffic to your hoplink. All major search engines will have a way for you to pay per click. Check the "Sponsored" sections, these are PPC ads that other people are paying for.
If you click one of these ads - then they will have to pay. This works on the basis that if you send enough visitors, one visitor will eventually buy the product and that product price (say $50) will be more than the price of the clicks (say $5).
Therefore the person returns a profit!
Affiliates! Bear in mind Google Adwords frowns upon Download products. You can try them by all means, however your best bet is Microsoft Adcenter or try one from this list below: They are all excellent alternatives and you can product great results!
Don't forget to test which ads are performing the best and then copy and slightly alter that ad - to find even better performing ads. Your CTR (Click-Through Ratio) will show you the number of clicks per number of searches that have been made.
The better the CTR - the more clicks you'll get!