please explain this code

public class Card
{
    // instance variables
    private int value;
    private String suit;

    /**
     * parameterized Card constructor
     * gets called when an object of the Card class is instantiated sending a number
     * as an argument - it determines the value and suit of the card based upon the
     * number received
     * @param num a number that gets converted to a value between 1 and 13
     * and one of the four suits (clubs, diamonds, hearts, or spades)
     */
    public Card(int num)
    {
        int suitNumber;
        value = num % 13;
        if (value == 0)
            value = 13;
        suitNumber = num / 13;
        if (suitNumber == 0)
            suit = new String("clubs");
        else if (suitNumber == 1)
            suit = new String("diamonds");
        else if (suitNumber == 2)
            suit = new String("hearts");
        else if (suitNumber == 3)
            suit = new String("spades");
        else
            suit = new String("ERROR");
    }

    /**
     * getValue method - returns what's stored in the instance variable value
     * @return the state of the instance variable value
     */
    public int getValue()
    {
        return value;
    }