The include statement will bring in a library of functions when the program is compiled that will contain all the routines required to run the program. Now we have the start of the main part of the program denoted by MAIN which must be followed by the brackets. The open bracket shows the compiler that there is a block of code to come. Leaving this out will give all kinds of funny compile errors. The bracket then closes and the program ends.
Most books make no mention of functions until half way through.
I prefer to introduce functions at the beginning. Take a look at the next program. MAIN is also a function but it is one that the compiler expects to find at the beginning. I'll go deeper into this at a later date. So just sit back a moment and reflect on what I've just said.