The preprocessor directive, in this case the include iostream, includes the iostream library to the set of code we will be writing so the compiler understands what we are writing.
The main function is the function that enables you to begin writing statements for the compiler to read.
Expression statements are expressions that end with a semicolon and are parts of the code that will be printed once complete.
Declaration statements are declarations that tell the expressions what the variables within them are.
Finally, the return statement tells the code that it is finished and to return to the beginning if asked to run again.