Are all the programming sketches in this website?
No: that would mean everything has already been invented 8) . But if you look here and in the Playground you'll find tons of stuff.
Also, when you buy components you may find code (often in the form of libraries) to get you going. For example I bought a DHT11 temperature and humidity sensor and found that the maker has a connection diagram, sample code, and a link to a library here. I have it online on my Arduino server here.
If you want to try a sensor xyz that you may have acquired, very often if you Google "xyz arduino" you'll be surprised what you find in terms of diagrams and code.
My advice, if your finances allow, is to get one of the many starter kits around; there's an official Arduino one, but many suppliers have made up their own.