printf() is used to print something to the standard output (console). If you want to display something static, that doesn't change, you can just put it into the argument:
printf("Hello World!\n");However, if you would like to have there something that you do not know what exactly it is when you write the code (e.g. a result of a calculation), then you can include the value of variables to be displayed on the standard output as well. Just like in your example you use the scientific notation (%e) to print the ceiling of x.
Please, check the printf() to see all the available format options (e.g. integral numbers, floating point numbers, strings, pointers, hexadecimal numbers, etc).