2 Improvements to registration Process

During the user registration, when user types in a different password for "confirm password" box, page will be reloaded without a warning.

Also if the username or email is already being used, registration page will reload without an alert about what went wrong.

1. Inform the user about errors.
How can I modify the pages so that corresponding error notices, such as password mistypes or email already being used, are provided ?

2. Add progress indicator
Also I want to include a progress indicator for the registration process. The part where user creates username & password should be labeled "Step 1" and the part where they click on payment button as "Step 2",...