Help: Pop-up for facebook creditental

I have a page to make automation with watir-webdriver using firefox.

for entering facebook credential I need to enter email ids, and how to click on the button of any pop ups…I have never used pop ups and I am completely a new comer in this field.

but I dont to how to enter email id in pop ups.

pop up url:

go to get there is an excellent screen cast ypu can
follow that