PPC results are usually in a different area of the results page listed as "sponsored" ads or results. These sponsored results are typically the top two or three results as well as results in the right margin. Results not appearing in the sponsored area are called "organic" results.
NOTE: Organic results receive a 5:1 click ratio over sponsored results. Therefore users are five times MORE likely to click on non-paid ads.
It is also important to define the term impression vs. a click. Let's say there are 5,000 monthly searches for your PPC keyword. If you have cornered the market on the keyword, your ad should appear to 5,000 searchers. It is similar to an ad in a magazine with a local circulation of 5,000. Or think of it as the number of people who drive by a highway ad sign. The impression means someone has had a chance to see your ad, but may not necessarily actually read it.
A click-through means someone saw your impression and actually clicked on the ad and visited your site. Some search engine PPC programs may or may not charge for impressions as well as click-throughs - though at a much lower rate.