用于iPhone应用的仪器UI自动化测试

I'm a newbie in UI Automation using instruments and I have the following question: - the application starts and I get the mainWindow screen (which contains SignIn and Register buttons) - I've managed to write the JavaScript code in order to tap one of the two buttons. -> after tapping one of the buttons, another screen is displayed. let's say the Sign In screen which contains two fields: username and password.I'm a newbie in UI Automation using instruments