The first step to enable two-factor authentication is to click on your account name in the upper right hand corner of the page and select "Security" from the drop down menu.
This will present you with the Security page. On the left will be a column with a similar list of options and in the main panel you should see a couple of options. The second line tells whether or not you have 2FA enabled, and provides a button to enable or disable it.
In this case, 2FA has not yet been enabled. Clicking on the "Enable" button will create a pop up window like the one below.
The QR and alphanumeric codes have been blurred, normally these will be visible. This is your best opportunity to back up this code. Read more about this here before continuing. Depending on which software you are using, there will be slight variations in what happens next. You will need to either use your device's camera to scan the QR code or enter the alphanumeric code manually into your app. Some apps will ask you to name your account next. Then you should be given a six digit code accompanied by a timer. When the timer runs out the current code expires and a new one will be generated. Make sure you have enough time left to enter the full code, then type it into the box at the bottom of the pop up window and click Enable. If you have entered the correct code the window will disappear and you will get a message in the upper right hand corner of the page.
It is worth noting that 2FA codes will be necessary for a number of changes that you wish to make, including turning other security features on and off, adding or renaming wallets, and other features.
On the Security page you will see that 2FA is enabled, as well as a Disable button to turn it off.
Clicking on the Disable button will bring up a pop-up window that asks for a 2FA code to verify that you are the legitimate owner of the account and that you wish to deactivate your additional security.
Simply enter the current verification code from your 2FA app and click the Disable button. You should get a confirmation message in the upper right of the page.
There are many different options for 2FA apps, as well as some hardware solutions. While we are not able to cover them all, we provide basic information about two of the most popular, Authy and Google Authenticator. However, we encourage everyone to do their own research and find the solution that is right for them.