Implementing Composite Design Pattern

I need to implement the Composite Design Pattern for this java code that is not complex but badly written. I am not sure where to start, I understand the concept of the design pattern but not sure which elements I'm going to need to take this code and use it to implement the composite design pattern.

public class RiverDiscoverer {

/**
* Main method to run this program.  
*
* @param args Unused in this code.
*/
public static void main(String[] args) {

Scanner input = new Scanner(System.in);
ArrayList<Integer> lengthsBetweenConvergences = new ArrayList<Integer>();
ArrayList<String> convergenceNames = new ArrayList<String>();
ArrayList<Integer> riverFlows = new ArrayList<Integer>(); //amount of flow on the main branch at each part of the river.



//get the main river's name
System.out.println("You have found the mouth of a new river where it spills into the sea. What do the locals call this river?");
String riverName = input.nextLine();
convergenceNames.add(riverName);

//measure the amount of flow
while (true) {
System.out.println("How much water is flowing into the sea? (L/s)");
try {
int flow = Integer.parseInt(input.nextLine());
riverFlows.add(flow);
break;
} catch (NumberFormatException e) {
System.out.println("I didn't understand that!");
}
}

while (true) {
System.out.println("How far did you walk until you reached the next junction? (in km)");
try {
int length = Integer.parseInt(input.nextLine());
lengthsBetweenConvergences.add(length);
} catch (NumberFormatException e) {
System.out.println("I didn't understand that!");
break;
}
System.out.println("Are you done traveling upstream on the " + riverName + "? (y/N)");
if (input.nextLine().equals("y")) {
System.out.println("Great! We're done!");
break;
} else {
System.out.println("That means you must be at another confluence. What is the name the locals have given the river flowing into this one?");
String tributaryName = input.nextLine();
convergenceNames.add(tributaryName);

System.out.println("How much water is flowing from that tributary into the main river? (L/s)");
while (true) {
try {
int flow = Integer.parseInt(input.nextLine());
int previousFlow = riverFlows.get(riverFlows.size() - 1);
riverFlows.add(previousFlow - flow);
break;
} catch (NumberFormatException e) {
System.out.println("I didn't understand that!");
}
}
}

}

//now print the results
System.out.println("You have now explored the " + riverName + "!");

//calculate the total length
int totalLength= 0;

for (Integer length : lengthsBetweenConvergences) {
totalLength += length;
}

System.out.println("The river is at least " + totalLength + " km long.");
System.out.println("From the furthest distance we explored:");

System.out.println(riverFlows.get(riverFlows.size() - 1) + " L/s flows " + lengthsBetweenConvergences.get(riverFlows.size() - 1) + " km downstream.");
System.out.println("Then, the " + convergenceNames.get(riverFlows.size() - 1) + " flows into the river.");

for (int i = riverFlows.size() - 2; i > 0; i--) {
System.out.println("Then " + riverFlows.get(i) + " L/s flows " + lengthsBetweenConvergences.get(i) + " km downstream.");
System.out.println("Then, the " + convergenceNames.get(i) + " flows into the river.");
}
System.out.println(riverFlows.get(0) + " L/s flows " + lengthsBetweenConvergences.get(0) + " km downstream.");
System.out.println("Then the " + riverName + " flows into the sea.");


    } 


    }

I understand how the Composite Design Pattern works but I dont know where to start refactoring and making changes... Any input to help push me in the right direction would help.