2. Squidoo has tier system for making money. Every lens has its own lensrank, calculated from many factors: freshness, traffic, sales, outclicks, time (visitor's) spent on lens, ... In general quality and quantity of traffic can guarantee high tier position. So you can earn money even without selling anything. This money comes from advertisers.
3. Selling stuff on Squidoo is easy. There are numerous selling modules available (Amazon, Ebay, Zazzle...) and you can also place your own affiliate links in text modules if you have basic html knowledge.
4. You can sell lenses on Squidoo. It is extremely easy. You only need to push a button for transfer a lens from your to somebody else's account. Or you can buy a lens. Prices vary. I have seen lenses for 3 and lenses for 3 thousand US dollars. Fresh lens, made from scratch is in general cheaper. Well matured lens with good backlinking background and a lot of already made sales and high tier position can be a real money maker, so price is higher.
Update: on 28 February 2013 Squidoo turned the ability of lens transfer off. There are still ways to buy or sell a lens but now they are much more complicated.
5. You can support your on-line business with Squidoo lenses. With presentation come powerful links and I have used Squidoo mainly for this purpose.
Before I discovered this site, my e-store was about 100 in SERP for my main keyword and nowhere for others. Now it is on first page for all keywords and I have several number one positions, in one case for some time I even had first seven positions for one longtail!
Update: on 28 March 2013 Squidoo made all links pointing out of Squidoo nofollow. This drastically reduced the site's potential for SEO purposes.