How to reference variables in other classes

I just feel like I'm not doing this correctly and I have researched and just can't seem to wrap my head around how to initialize variable that have to reference another method or class.

Player class

public class Player
{
   //instance variables
   private String name;
   private ScoreCard card;
   private int fullDriveYards;
   private int fullDrives;
   private int drivesOnTarget;
}

Here's the ScoreCard class variables

public class ScoreCard
{
    private int totalStrokes;
    private int versusPar;
    private LinkedList<Integer> playerScoreCard;
}

So this is how I have initialized the instance variables is Player class I did not code the Scorecard class as I didn't have to but I still added it so you can see what's going on. I just need to know if I am on the right track or completely off.

// Constructor for objects of class Player
public Player(String PlayerName)
{
       // initialize all instance variables
       // look for and handle a null reference for playerName
       // to initialize this.card create ScoreCard instance and assign reference
       this.name = PlayerName;
       PlayerName = "UNKNOWN";
       ScoreCard card = this.card;
       this.card = new ScoreCard();
       this.longestDrive = 0;
       this.fullDriveYards = 0;
       this.fullDrives = 0;
       this.drivesOnTarget = 0;
}

"I just feel like I'm not doing this correctly ..."

It's correct, there are just some inconsistencies, so you may not get the result you're looking for.

In your constructor method for Player, you are assigning PlayerName to the name field, and then subsequently assigning PlayerName to "UNKNOWN".

Assigning PlayerName will have no effect on name.

this.name = PlayerName;
PlayerName = "UNKNOWN";

In your comment you mention,

// look for and handle a null reference for playerName

You'll need a conditional statement for this.

if (PlayerName == null) PlayerName = "UNKNOWN";
this.name = PlayerName;

Furthermore, you are assigning your class variable card to a new local variable card.

This, again, will have no effect, since this.card would be null at this point.

// to initialize this.card create ScoreCard instance and assign reference

The following will suffice.

this.card = new ScoreCard();

So, the complete constructor should look like the following.

public Player(String PlayerName)
{
    // initialize all instance variables
    // look for and handle a null reference for playerName
    // to initialize this.card create ScoreCard instance and assign reference
    if (PlayerName == null) PlayerName = "UNKNOWN";
    this.name = PlayerName;
    this.card = new ScoreCard();
    this.longestDrive = 0;
    this.fullDriveYards = 0;
    this.fullDrives = 0;
    this.drivesOnTarget = 0;
}

"... I have researched and just can't seem to wrap my head around how to initialize variable that have to reference another method or class. ..."

You're assignment is correct,

this.card = new ScoreCard();

Since you're ScoreCard class variables are declared as private, you won't be able to access them via dot-notation—e.g., card.totalStrokes.

You will need to either remove the modifier, change the modifier to public, or create methods that will provide the access.

public class ScoreCard
{
    private int totalStrokes;
    private int versusPar;
    private LinkedList<Integer> playerScoreCard;

    public int getTotalStrokes() {
        return totalStrokes;
    }

    public void setTotalStrokes(int totalStrokes) {
        this.totalStrokes = totalStrokes;
    }

    public int getVersusPar() {
        return versusPar;
    }

    public void setVersusPar(int versusPar) {
        this.versusPar = versusPar;
    }

    public LinkedList<Integer> getPlayerScoreCard() {
        return playerScoreCard;
    }

    public void setPlayerScoreCard(LinkedList<Integer> playerScoreCard) {
        this.playerScoreCard = playerScoreCard;
    }
}

Then, you can access the values as follows.

card.setTotalStrokes(123);
card.setVersusPar(123);
card.setPlayerScoreCard(new LinkedList<>());

Here are some references by Java which may help in your coding process.

Classes (The Java™ Tutorials > Learning the Java Language > Classes and Objects).
Lesson: Object-Oriented Programming Concepts (The Java™ Tutorials > Learning the Java Language).