The CCompilerDriver package lets you work with C compilers that are installed on your computer. It is used automatically by the Wolfram System compiler when you set the option CompilationTarget to "C", but you can use it to build your own executables, libraries, and object files from source code written in the C language.
If the input came from one or more files of C code, these could be given to CreateExecutable in a list.
More information on options and settings is found in the section on Configuring the Compilation.
WSTP is the Wolfram Language's unique high-level symbolic interface standard for interprogram communication. The CCompilerDriver package is useful for working with WSTP since you can build WSTP programs from within the Wolfram Language. One particularly useful feature is that if an input file is given with an extension of .tm, CreateExecutable will treat this as a WSTP template file and use mprep to process it.
More information is found in the WSTP documentation.