I had found from the manual that Sprog DCC controller using as USB to serial converters, therefore USB host shields should be able to support.

you need to debounces the input, without which pressing the button once would appear to the code as multiple presses.
http://www.arduino.cc/en/Tutorial/Switch

Code:

int led1 = 13;
int led2 = 12;
int led3 = 10;

void setup(){
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
 
}
void loop(){

  pinMode(led3, INPUT); //this does not work ??? why???
  digitalWrite(led1,HIGH);
  digitalWrite(led2,LOW);
  // digitalWrite(led3,LOW); --> If you already set it to input, don't write
  delay(500);
 
  pinMode(led3, OUTPUT); //this does not work ??
  pinMode(led1, INPUT); //this does not work ??
  // digitalWrite(led1,LOW);  --> If you already set it to input, don't write
  digitalWrite(led2,LOW);
  digitalWrite(led3,HIGH);
  delay(500);
 
  pinMode(led1, OUTPUT); //this does not work ??
  pinMode(led2, INPUT); //this does not work ??
  digitalWrite(led1,HIGH);
//  digitalWrite(led2,HIGH);  --> If you already set it to input, don't write
  digitalWrite(led3,LOW);
  delay(500);
 
  pinMode(led2, OUTPUT); //this does not work ??
  pinMode(led3, INPUT); //this does not work ??
  digitalWrite(led1,LOW);
  digitalWrite(led2,HIGH);
//  digitalWrite(led3,HIGH);  --> If you already set it to input, don't write
  pinMode(led3, OUTPUT); //this does not work ??
  delay(500);

}

Read this, the Arduino USB Host shields was design as the hardware interface, but the supported device was up to the user who use it to write the interface software to talk to a USB device.

USB in a NutShell

Making sense of the USB standard
Starting out new with USB can be quite daunting. With the USB 2.0 specification at 650 pages one could easily be put off just by the sheer size of the standard. This is only the beginning of a long list of associated standards for USB. There are USB Class Standards such as the HID Class Specification which details the common operation of devices (keyboards, mice etc) falling under the HID (Human Interface Devices) Class - only another 97 pages. If you are designing a USB Host, then you have three Host Controller Interface Standards to choose from. None of these are detailed in the USB 2.0 Spec.

USB defines class code information that is used to identify a device’s functionality and to nominally load a device driver based on that functionality.

Some of the USB device like the cheap wi-fi dongle, have only RF transceiver in the hardware, the wifi protocol and IP stack was all in the device driver, hence you are unlikely to get it work with Arduino, perhaps too large to fit in the AVR micro's flash.

For example I was tempted to recommend an Arduino to control model trains using a Sprog dcc controller (which connects to a PC by USB) but I realized I had no way of knowing whether it would work with an Arduino, or even what to look for in the product specifications that would help me to know.

To know the protocol for Sprog dcc controller, You will have to get a USB sniffer to be able to sniff the protocol.

You need to include this a the start of the code

Code:

#include "Arduino.h"

Yes, but you may not need the 10K resistors to Gnd.
http://playground.arduino.cc//Code/Keypad

Serial.begin( 115200 );

You have to set your serial to 115200 baud, by default is only 9600 baud.

[Do not cross post!]

Do not cross post!

https://github.com/felis/USB_Host_Shield_2.0/blob/master/examples/board_qc/board_qc.ino
The board_qc sample in the Host Shield 2.0 library is use to test your board.  It out on serial with 115200 baud.

What device are you connected to this USB host shield?

http://theoldrobots.com/arms2.html
http://theoldrobots.com/book40/Movit_Robot_Arm_MR-999E.pdf
Base on the schematic diagram, the robot arm used two 3V batteries form a double-ended power supply for the motors.
You can use two transistors to control the motors like this

http://arduino.cc/forum/index.php?topic=96204.0

New version 0.6k on line 
- Some fix (By PaoloP)

The link 404 not able to download

Have you try the New LCD library?
http://playground.arduino.cc//Code/LCD

New LCD library - Replacement for the original LiquidCrystal Library to control LCDs with different control interfaces: 4bit, 8bit, I2C, ShiftRegister, SPI comming soon. The library is faster than the original, more flexible and extendable.

i whant to run 6 LED's on three outputs but then i have to disable one of the pins.

Are you doing Charlieplexing
Try this Library
http://playground.arduino.cc/code/charlieplex

http://arduino.cc/forum/index.php/topic,41318.0.html
http://avrcryptolib.das-labor.org/trac

This is a N-channel MOSFET, the Source pin has to connected to ground and the Drain connect to the valve, the other side of the valve connect to 12V.