Tic Tac Toe Help

I just recently completed a tic tac toe program that I wish to change so that it uses classes. Can someone give me a hand in how I should do this? I have never used classes before in my programs and need to have an idea of how they work.
Here is my code

Code:

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#include <iostream>
#include <cstdlib>
#include <time.h>

using namespace std;
int option, test, row, col, turn, option2 = 0;
char board[3][3];

//Prints the board to the screen
void drawBoard()
{
    cout<<"\n";
    for(int i = 0; i < 3; i++)
    {
        for(int j = 0; j < 3; j++)
        {
                cout<<"|"<<board[i][j]<<"|  ";
        }       
        cout<<"\n-------------\n";
    }       
}   

//Function checks for a winner if the returned is: 1 if X wins, 2 if O wins, 3 if tie
int checkWinner()
{
//Checks to see if X won   
        int r=0;
       
        //Checks for all possibilities for X to win in rows
        if(board[0][0] == 'X' && board[0][1] == 'X' && board[0][2] == 'X')
          r=1;
        if(board[1][0] == 'X' && board[1][1] == 'X' && board[1][2] == 'X')
          r=1;   
        if(board[2][0] == 'X' && board[2][1] == 'X' && board[2][2] == 'X')
          r=1; 
                     
        //Checks for all possibilities for X to win in columns
        if(board[0][0] == 'X' && board[1][0] == 'X' && board[2][0] == 'X')
          r=1; 
        if(board[0][1] == 'X' && board[1][1] == 'X' && board[2][1] == 'X')
          r=1;
        if(board[0][2] == 'X' && board[1][2] == 'X' && board[2][2] == 'X')
          r=1;         

        //Checks for all possibilities for X to win diagonally
        if(board[0][0] == 'X' && board[1][1] == 'X' && board[2][2] == 'X')
          r=1; 
        if(board[2][0] == 'X' && board[1][1] == 'X' && board[0][2] == 'X')
          r=1; 
//Checks to see if O won
        //Checks for all possibilities for O to win in rows
        if(board[0][0] == 'O' && board[0][1] == 'O' && board[0][2] == 'O')
          r=2;
        if(board[1][0] == 'O' && board[1][1] == 'O' && board[1][2] == 'O')
          r=2;   
        if(board[2][0] == 'O' && board[2][1] == 'O' && board[2][2] == 'O')
          r=2; 
                     
        //Checks for all possibilities for O to win in columns
        if(board[0][0] == 'O' && board[1][0] == 'O' && board[2][0] == 'O')
          r=2; 
        if(board[0][1] == 'O' && board[1][1] == 'O' && board[2][1] == 'O')
          r=2;
        if(board[0][2] == 'O' && board[1][2] == 'O' && board[2][2] == 'O')
          r=2;         

        //Checks for all possibilities for O to win diagonally
        if(board[0][0] == 'O' && board[1][1] == 'O' && board[2][2] == 'O')
          r=2; 
        if(board[2][0] == 'O' && board[1][1] == 'O' && board[0][2] == 'O')
          r=2;
       
        if(r==1)
          return 1;
        if(r==2)
          return 2;

//Checks for a tie
        int s=0;
        int i, j;
        for (i=0; i<3; i++)
        for (j=0; j<3; j++)
        {
        if ((board[i][j] == 'X') || (board[i][j] == 'O'))
        s++;
        }
        if (r!=1 && r!=2 && s==9)
          return 3;
                                               
}       
//Computer generates a random move and see if it's available. If it is, then the move is made.
//If it isn't then it generates another random move.
void Computer()
{
    col = -1;
    row = -1;
    while(col == -1 || row == -1)
    {
        time_t seconds;
        time(&seconds);
        srand((unsigned int) seconds); 
        col = rand()%3;
        row = rand()%3;
        if(board[row][col] != ' ')
        {
            col = -1;
            row = -1;
        }
        board[row][col] = 'O';                       
    }         
   
}   
int main()
{

    do
    {
      option2 = 0;//Allows the game to be played multiple times.
      cout<<"Enter a menu option:\n";
      cout<<"-----------------------------\n\n";
      cout<<"1. Play Tic Tac Toe\n";
      cout<<"2. Quit\n";
      cin>>option;
      for(int i = 0; i < 3; i++)
      {
          for(int j = 0; j < 3; j++)
          {
                  board[i][j] = ' ';
          }       
      }   
      if(option !=2)
      {
        while(option2 != -1)//Game will continue until someone wins or it is a tie.
        {       
            if(turn%2 == 0)//If it's even then it's X's turn.
            {
                bool condition = true;
                while(condition == true)
                {   
                    cout<<"\n\nEnter a move:\n";
                    cout<<"Enter the row you wish to make your move on (0,1,2)\n";
                    cin>>row;
                    cout<<"Enter the column you wish to make your move on (0,1,2)\n";
                    cin>>col; 
                    if(board[row][col] == ' ')//Checks to see if the move is valid
                    { 
                        board[row][col] = 'X';
                        turn++;
                        condition = false;
                    }   
                    else
                        cout<<"Invalid move!\n";
                }   
            }   
            else//The computer makes a move.
            {
                Computer();                 
                turn++;
            }
                         
            if(checkWinner() == 1)//X wins
            {
                cout<<"Congratulations! You won!\n\n";
                option2 = -1;
            }             
            else if(checkWinner() == 2)//O wins
            {
                cout<<"Sorry, but the computer won.\n\n";
                option2 = -1;
            }             
            else if(checkWinner() == 3)//It's a tie
            {
                cout<<"It seems we have a tie.\n\n";
                option2 = -1;
            }
            drawBoard();
        } 
       
      } 
     
    }while(option != 2);
      cout<<"\n\n\n\nPress Enter to quit.";
      cin.get();
}

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