Being able to print simple text strings is good, but not nearly enough. The first argument to the 'printf' command must always be a character string, but any number of additional arguments may be provided. Now, these additional arguments may be number constants, other character strings, variables, etc., and may be output in the resulting string by referencing them with 'specifiers' placed within the first example. One example of a specifier is '%i' which is shorthand for saying 'an integer value' - if used within the character string provided to printf, the command will expect an integer constant or variable to be provided as an additional argument. For example:

printf("This number is %i.\n", 10);

will print

This number is 10.

Similarly,

int value = 1234;
printf("Constant is %i, variable is %i.\n", 10, value);

will print

Constant is 10, variable is 1234.

There are other specifiers suitable for different types of data. The way data is presented by the specifier in the final output can also be controlled (e.g. for numerical arguments the number of decimal places, presence of exponentiation, etc., can be defined).