The function `std::count` is part of the C++ Standard Library, specifically within the `<algorithm>` header. It is used to count the number of occurrences of a specific value in a range of elements, such as an array or a vector. The function takes three parameters: the beginning and ending iterators of the range, and the value to count. To use `std::count`, you typically include the necessary header and call the function with the appropriate arguments. For example, if you have a vector of integers and want to count how many times the number 5 appears, you would pass the vector's begin and end iterators along with the value 5 to `std::count`.