The document discusses different types of header files, character functions, string functions, math functions, and random functions available in C/C++ libraries. Header files provide function prototypes, library definitions, and standard input/output streams. Common header files include stdio.h, string.h, math.h, and stdlib.h. Character functions check properties like whether a character is a letter, digit, lowercase, or uppercase. String functions allow concatenation, comparison, copying of strings. Math functions perform tasks like absolute value and remainder calculations. Random number generation functions generate random numbers within a range.