The below description will show you that there are two ways to log into the website:
The facebook login allows you to log into the website without much hassle. You do not need to remember the password (ie don't have an extra password to remember in your already long list of passwords). Furthermore, the website will log you automatically into the website whenever you are logged into facebook and are on the website. No more annoying entering of password...
This login, as the name suggests, is the standard one that is used on all kind of websites. You need to enter the details necessitated and then the website will send you a link back to activate your account. The standard way...
If you want to change your password or the email that is used to send out updates, you can change it over your profile on the website (see the Help on Profiles).