World.placeNSWall(), World.placeEWWall() have three parameters (sometimes called arguments). You need to tell these methods three integers, For a East-West Street: the number of the street, the number of the Avenue, and the length of the wall (either going East or North, depending on the direction. Once you get the hang of reading the API of a class you can quickly use or build upon other people's code (or even your own).

import kareltherobot.*;
public class Walls implements Directions {
	public static void task() {
		Robot karel = new Robot(1, 2, East, 0);
		karel.move();    
		karel.move();	  
		karel.pickBeeper();   	                
		karel.move();	  
		karel.turnLeft();	  
		karel.move();
		karel.move();	  
		karel.putBeeper();  
		karel.move();
		karel.turnOff();
 
	}
	// Main entry point
	public static void main(String[] args) {
		World.setDelay(150);
		World.setSize(8, 9);
		//World.readWorld("first.kwld");  
		World.placeBeepers(1, 4, 1);
		World.placeEWWall(3, 1, 3);
		World.placeNSWall(1,6, 5);
		World.placeEWWall(6, 1, 6);
		World.setVisible();
		task();
	}
}

You can make a long string and send it all at once to the World. :

public static void main(String[] args) {
		String hurdles = "streets 8\n" + 
				"avenues 9\n" + 
				"eastwestwalls 3 1 3\n" + 
				"northsouthwalls 1 6 5\n" + 
				"eastwestwalls 6 1 6\n" + 
				"beepers 1 4 1";
		World.getWorld(hurdles);
		World.setVisible();
        task();
	}

You can place a text file with these string commands, give the file a name, and add it to your project and use the call <code java> World.readWorld(“second.kwld”);