Here's the initial code for C:

char *smash (const char *const words[/* count */], size_t count)
{
// allocate a string on the heap, memory will be freed
	return calloc(1, 1);
}

This is what you need to implement. A function named smash that returns the result. You don't need to write main() or accept input using scanf.

Here's a Python example how the platform works: https://docs.codewars.com/training/training-example

It is not how problems with kata should be reported.