Q: "Why is this site free? What's the catch? How do you make money?"
Many people are curious or even suspicious about the fact that everything on this website is free. Don't worry, there are no hidden catches or nasty surprises. The reason we can make all this free is that it's supported by advertising. The business model is quite simple: We attract as many visitors as possible to the website, and for each visitor we make a tiny amount of money (less than 1 cent) by showing them an ad or two.
Of course we could charge visitors to access our material. Plenty of websites do that and it works well for them. We have no problem with the paid model but we've just decided that the free model suits us better.
Caveat: We are planning to introduce a paid app. Unfortunately we do need to charge for this to cover development costs.
Q: "Can I do the same thing with my website?"
When people learn how we make money, a common response is to ask if they can do the same thing as us. The answer is "maybe", but here's the thing: You need thousands of visitors per day to make it worthwhile. If your website gets less than a thousand unique visitors per day it's probably not worth your time implementing ads.