What's the working of first(a), second(b){ } in the code?

Question

template <class T>
class Pair {
private:
T first, second;
public:
Pair (T a, T b):
first(a), second(b){
}
T bigger();
};

template <class T>
T Pair<T>::bigger() {
// some code
}

Answer 1

initialization of variables before constructor is called, this is the only way to initialize const T& class variables