Add simple function to a script

I have a script demo here: [login to view URL] about functions script: +) When a people enter email and payment, after payment, people will get a mail will link download a product (featured: file protection, anti-cheat price) Now i want add some functions to this script, (easy but i'm not coder ): i want +) When people enter mail and payment, after payment, people will get a mail with a password (auto generator ) , have not link download. +) Member can go to my website and login with email and password (got on mail) and go to download product page. +) and on member main page, have function: step 1: enter domain name on a input, and click save button step 2: system will generator a product key, and add domain, product key to database (table of member buyer). +) member can change password and logout +) of couse, when member has login, can go to shop and buy more, not send mail with pass again. +) and of couse, on admin page, admin can change member info or domain name, product key! just it, i say maybe not easy understand. i have attachment a image about my want to! and, attachment script too!