Signing in on the website
On the website you sign in with an email address and a password. You can also sign in with a Google account, and that is the short way: it needs no password, and the address arrives already verified.
If you registered with an email and a password, a confirmation email is sent to you. Until you confirm the address you cannot sign in with it and a password. You can ask for the confirmation email again from the settings page.
The password is at least eight characters. If you forgot it, there is a reset link on the sign-in page, and it sends you a recovery email.
You can change your password from your account settings. Changing the password signs out every other session on the account, so a device you forgot about is disconnected.