With two-factor login (2FA), you'll be asked for a 6-digit code from an authenticator app every time you log in, in addition to your password. It's completely optional, but recommended, especially if you've saved a card for automatic invoice payments.
Here's how to set it up:
1. "My Account" → "Security" tab → "Set up / manage" (or "Two-Factor Login" in the menu)
2. Scan the displayed QR code with an authenticator app (for example Google Authenticator, Authy or 1Password) or enter the secret manually
3. Enter the 6-digit code currently displayed to confirm
From your next login on, you'll be asked for the code. On the same page, you can turn off two-factor login again, sign out all other logged-in devices ("End all other sessions") and view your recent login attempts.