Phishing Website

Well, i've been reading some books and stuffs about phishing and i learned alot BUT there is something i need help with, i know how to make a phishing page etc... but when the victim will log in of course he will be redirected to the real website or somewhere else, My question is: How can i make a "script" or something that when the victim enter his creds the script will automatically login to the real website and redirects him there so he doesn't suspect anything, I know a tool that could do this but in my case i want to know how to do it manually...