One of the best pieces of security advice any computer expert can give you is to enable two-factor authentication for websites that support it. With password breaches so common nowadays, it could be the one thing that keeps hackers from stealing your identity online. Here are five points to help you understand this technology.Two-factor authentication or two-step verification?A lot of people think they're the same thing, but that's not really accurate.There are three types of authentication factors: something you know, such as a password or PIN; something you have, such as a mobile phone or a special USB key; and something you are, such as your fingerprint or other biometric identifier.While two-factor authentication combines two different factors, two-step verification uses the same factor twice, for example a password and a one-time-code sent via email or SMS.You might think a code sent to a phone qualifies as a second factor, since the phone is something you physically have, but SMS is insecure and the code can be intercepted. From a security risk perspective, that makes it similar to a password.While two-factor authentication is more secure than two-step verification,\u00a0both are better than relying on a single password. So regardless of which one is on offer, take advantage of it.One account that rules them allIf there's one online account that's worth protecting above all others, it's your email. That's not just because it contains your private conversations, but because it serves as a gateway to your other accounts.Most online services ask users to sign up with email, and rely on that to reset passwords and send important communications. An attacker with access to your email can search for old registration emails and find out where you have accounts online. He can then reset passwords and communicate with technical support staff at those websites.Start your adoption of two-factor or two-step authentication by turning it on for your email. All the large email providers including Gmail, Yahoo and Outlook offer this.I did that, now what?If you're using a password manager, make that your next priority. The most popular password managers have a two-factor authentication option.Then enable it at other sites. Many popular services support two-factor authentication, including Facebook, Twitter, Apple ID, iCloud, Amazon, PayPal, LinkedIn, Snapchat and WordPress.com. Mobile identity provider TeleSign has set up a website at www.turnon2fa.com with detailed tutorials for enabling two-factor authentication at many of those services.To trust or not to trustMost websites that support two-factor authentication allow users to mark devices as trusted when they authenticate for the first time using both factors. This essentially disables two-factor authentication for those trusted devices, and allows the user to authenticate with only their password in future.This is good for usability, but it's not great for security. If you turn off two-factor authentication for a trusted device, you can make it easier for hackers to access your accounts, so you should be aware there is a trade-off.There's also the fact that if you lose your phone or computer, you can't be certain that the thief won't find some way to unlock it.Fortunately, most websites give users the option to remove any of their previously trusted devices in case they are lost or compromised, so keep that in mind.Do I risk locking myself out?In most cases, your phone will be central to your two-factor authentication experience. It will be used either to receive codes by SMS or to generate them using special apps like Google Authenticator. But phones are easily lost, stolen or broken.The good news is that most online services have contingency plans for those scenarios. Some companies allow users to specify a backup phone number that can be used for account recovery. Others provide backup codes when turning on two-factor authentication that can be printed on paper and kept in a safe place.If these options fail, you will most likely have to call or email the company's technical support department and prove the account is yours, for example by providing information about the account that only you would know. Either way, getting completely locked out of an account is extremely rare.