Two-factor Authentication (2FA) is an extra layer of security for your account that can be utilized to ensure that you are the only person who can access your account and perform account actions such as depositing, withdrawing, or trading, even if someone obtains your username and password.
When enabled, the way 2FA works, is that any login attempt on your account, or attempted account action, such as depositing, withdrawing, or trading, requires an extra passcode to be entered in addition to the username and password. This extra passcode is usually stored in an app on your phone and is regenerated every 30 seconds. It is also possible to use a security key such as a Yubikey for 2FA.
The benefit of enabling 2FA on your account is to protect against attackers, as any attacker would not only need the username and password to log in to your account, but also be in possession of your 2FA device to access your account and/or perform account actions such as depositing, withdrawing, or trading.
For example, if your 2FA codes were stored on your phone, the attacker would need possession of your phone in addition to your username and password.