Please post the code when answering

Create a sign in or log in page. The user should see two forms. Form 1 will enable the user to sign in to the system by providing an account name and a password. When the user provide account name and password then click on submit button to sign in, a PHP page will take the account name and the password and verify if account name already exists in the database. If account exist, notify the user that account already exists and to try again by pressing the back button on the browser. If the account does not exists, insert the account and password into the database and tell the user that account created and that they need to login to the system. Form 2 will enable the user to login to the system. When the user provide account name and password then click on submit button to sign in, a PHP page will take the account name and verify if account name already exists in the database. If the account does exist, then verify if the password in the database matches the password entered by the user. If the passwords match, inform the user of a successful login. If the passwords do not match, let the user knows invalid password. if the account does not exist, let the user knows that invalid account.