The rand function in C generates pseudorandom integers ranging from 0 to RAND_MAX, while srand is used to seed the pseudorandom number generator to produce different sequences of random numbers. The sleep function is not part of the C standard library but is available in GNU libc for pausing program execution. To generate random numbers within a specific range, the modulus operator can be used, such as rand() % 6 for numbers between 0 and 5. Properly using srand at the start of a program ensures varied results in repeated calls to rand. Understanding these functions is essential for effective random number generation in C programming.