If you give some details of what you're actually trying to do we could probably help. But trying to explain the entire language to you one statement at a time with no idea of why you want to know is way too much like hard work. There are plenty of Arduino and C++ tutorials, try the top of the page under Resources or the many example programs in the IDE.
OTOH if you have a real program in mind tell us what it's supposed to do, post your best attempt at it and say what problems you're having. Then we'll have something to start from.
Steve