Ok for me not to understand this program?

[DJLad16]

// Hangman
// The classic game of hangman

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <ctime>
#include <cctype>

using namespace std;

int main()
{
    // set-up
    const int MAX_WRONG = 8;  // maximum number of incorrect guesses allowed

    vector<string> words;  // collection of possible words to guess
    words.push_back("GUESS");
    words.push_back("HANGMAN");
    words.push_back("DIFFICULT");

    srand(static_cast<unsigned int>(time(0)));
    random_shuffle(words.begin(), words.end());
    const string THE_WORD = words[0];            // word to guess
    int wrong = 0;                               // number of incorrect guesses
    string soFar(THE_WORD.size(), '-');          // word guessed so far
    string used = "";                            // letters already guessed

    cout << "Welcome to Hangman.  Good luck!\n";

    // main loop
    while ((wrong < MAX_WRONG) && (soFar != THE_WORD))
    {
        cout << "\n\nYou have " << (MAX_WRONG - wrong);
		cout << " incorrect guesses left.\n";
        cout << "\nYou've used the following letters:\n" << used << endl;
        cout << "\nSo far, the word is:\n" << soFar << endl;

        char guess;
        cout << "\n\nEnter your guess: ";
        cin >> guess;
        guess = toupper(guess); //make uppercase since secret word in uppercase
        while (used.find(guess) != string::npos)
        {
            cout << "\nYou've already guessed " << guess << endl;
            cout << "Enter your guess: ";
            cin >> guess;
            guess = toupper(guess);
        }

        used += guess;

        if (THE_WORD.find(guess) != string::npos)
        {
            cout << "That's right! " << guess << " is in the word.\n";

            // update soFar to include newly guessed letter
            for (unsigned int i = 0; i < THE_WORD.length(); ++i)
			{
                if (THE_WORD[i] == guess)
				{
                    soFar[i] = guess;
				}
			}
        }
        else
        {
            cout << "Sorry, " << guess << " isn't in the word.\n";
            ++wrong;
        }
    }

    // shut down
    if (wrong == MAX_WRONG)
        cout << "\nYou've been hanged!";
    else
        cout << "\nYou guessed it!";
    
    cout << "\nThe word was " << THE_WORD << endl;

    return 0;
}

This is in the book I'm learning, and I feel that seen as I am up to the point of this program I should be able to understand it.
There's bit I get, and there's bits I don't get. I am still a beginner (been learning c++ for about 2-3) with a few weeks off due exams. I personally think it was quite a hard program to get introduced to, as it is basically a game without UI and graphics. And I'm still at the point where I'm only creating basic programs.

[devonrevenge]

what is it that you dont understand? i learnt vectors a bit late, but you knows arrays

[devonrevenge]

you could comfortably get this in a month?

[Chervil]

When it comes to understanding a program, you might consider it on two levels.

One is the overall flow and structure, that is, what the program is supposed to achieve. Then at a more detailed level, you might consider some of the individual statements, or small groups of statements. You don't necessarily need to hold the entire thing in your head simultaneously.