None of the personal information above will ever appear on the web pages. You will be assigned a randomly-generated username. This (not your own name) will appear alongside any group's details that you modify, but even that will only be visible to other known users. The site manager and no-one else will know to whom the username belongs. Of course the purpose of this is to block trolls and vandals, which will be done permanently and without warning.
You will not have to supply these details again, because you will be sent a cookie that identifies you to this website and automatically allows you to make modifications. (So there is no notion of "session" and you are effectively "logged in" permanently.)
This means that you must only fill in this form if you are using your own computer (or your own login on a professionally managed company or university system), not an Internet Café!
If you create a login using one computer and then want to log in using another, you will need to retrieve your cookie by repeating this process. For this, you must enter your name and postcode in exactly the same way again.
If your web browser is configured to delete cookies, you will need to whitelist this site or its cookie, otherwise you will have to re-fill this form every time you want to update some group's details.