Let me tell somebody that how we write test cases in selenium with php , with one simple example?

I just wanted to know how to do it, let me a take a login page or so, no examples in the selenium web site pleaseLet me tell somebody that how we write test cases in selenium with php , with one simple example?
a login page? check you need to enter data to login... check that the data is also valid, and the username/password is a valid combination - check error handling pages.