begin returns an iterator to the first element in the sequence container.

end returns an iterator to the first element past the end.

If the vector object is const, both begin and end return a const_iterator. If you want a const_iterator to be returned even if your vector is not const, you can use cbegin and cend.

Example:

#include <vector>
#include <iostream>

int main() {
    std::vector<int> v = { 1, 2, 3, 4, 5 };  //intialize vector using an initializer_list

    for (std::vector<int>::iterator it = v.begin(); it != v.end(); ++it) {
        std::cout << *it << " ";
    }

    return 0;
}

Output:

1 2 3 4 5