Sign in at /account/sign-in/ with your email address and password. There is no separate username.
If it will not let you in
A failed sign-in always says the same thing, that the email or password is incorrect, whatever the actual reason. That is deliberate: a more specific message would tell anyone typing addresses into the form which ones have accounts here.
Sign-in attempts are rate limited per email address and per source address, so after several failures in a row you may be asked to wait.
Reset the password
/account/password-reset/ emails a link to the address you enter. The link expires.
Password reset does not clear two-factor
Proving you control the email address says nothing about the second factor. If you have lost your authenticator and your recovery codes, resetting the password is not enough. Open a ticket. See Two-factor authentication and passkeys.
Signed-in sessions
/console/account/sessions/ lists your active sessions with the device and address each was created from, and lets you revoke any of them. Revoke everything after using a machine you do not control, or after a password change you made because of a leak.
Your profile
/console/account/profile/ holds your name, contact details and theme preference. The account email is the account identity, so changing it is a support request rather than a form.