Two-factor authentication adds a second step to signing in: after your password, you also enter a 6-digit code from an app on your phone. Even if someone learns your password, they can't sign in without your phone too.
Once confirmed, you'll see a set of recovery codes — save these somewhere safe (a password manager, printed and locked away). Each one works exactly once and gets you back into your account if you ever lose your phone.
You'll enter your password as normal, then be asked for a code from your app. If you don't have your phone, use one of your recovery codes instead — the security page always shows how many you have left.
Don't worry — you're not locked out permanently. Ask a team Admin or Owner to reset two-factor authentication on your account from the Team page (they'll need their own two-factor authentication confirmed first, as a safety check). If you're the only Owner and have no one else to ask, contact support.
From Security in the top bar, confirm your password and enter a current code to turn two-factor authentication off. Your administrator will be notified either way — turning it on or off is always recorded.