Functions in C++ are blocks of code that perform a specific task. They help in organizing code into manageable chunks and promote reusability. Understanding functions involves knowing how to declare and define them, pass arguments, return values, and handle function overloading.

Functions are declared using a function signature, which includes the return type, function name, and parameters (if any). The function definition contains the implementation of the function.

// Function declaration
int add(int a, int b);

// Function definition
int add(int a, int b) {
return a + b;
}