PPC (pay-per-click) is just that-- you are paying every time someone clicks on your ad. For example, using the hair care products example, if you are selling hair care product, you might be willing to pay for clicks that originate with the consumer clicking on the word "Shampoo" or "Conditioner" or "hair care products". The consumer that clicks on your link is already interested in hair care products, and has a much higher tendency to purchase the hair care products than the general public. You will pay a much higher price for this click thru than you would a click thru from a more general source. 

Search engine marketing involves using a more strategic methods to promote your site to one of the (preferably) top ten positions for a given search term (keyword). When someone searches for the hair care products, for example, your site will appear in one of the top ten listings. They click through to your site, this make them a more highly targeted viewer than the general audience. This requires a great deal of planning and work to get a top ten ranking. Keep in mind, that for most popular search terms, there may be millions of web sites related to that topic, and many of them are also using search engine marketing strategies to try and "beat the system". When you first begin; focus on creating a quality site with great and clear content.

Article marketing, is just that, you will write articles that relate to your site market, for example, hair care products or shampoo or great hair care. You will submit your articles to directories and web sites accepting new articles. At the end of your article, you will include a link back to your site, so that the interested readers can come to your site after reading information hair care products. This way, only the targeted reader, interested hair care products will click thru to your site.