The first thing to know about this program is that all the green text at the top, does nothing. It is just one long comment, there solely to give you information. It is always good programming practice to put lots of comments in your code, since later on, you won't have a clue what you were thinking at the time.
The big long comment at the top, you will see, begins with a "/*" and ends with a "*/" (all the other stars are simply there for show). This is how you do a comment that runs over a number of lines. Everything in between is completely ignored by the C compiler. You'll also notice a short comment on line 14, which says /* entry point */. (You can tell if you are on line 14, because the numbers at the bottom of the screen tell you which line and which character position the cursor is at.)
Another way to add a comment to your program is to type two forward slashes, "//". This will tell the compiler to ignore everything which follows-na on that particular line. This is convenient when commenting code, since after each line you can put a comment which explains what that line does.