Two Factor Authentication (2FA aka Multi Factor Authentication) allows for extra protection of your Side Door account.
For new users signing up, you'll be sent an email after entering your email and password to verify your email address.
If you do not disable 2FA, this will be required each time you log in again.
To turn 2FA on or off, simply click on your round user icon (bottom left on desktop, top right on mobile), then Settings > Account, where you can toggle this function on or off.