Two factor authentication is used to verify your identity by using a 2nd method to login besides just your username and password. For example, you may be asked to call a number from a specific phone number, or a text message code will be sent to your phone to enter after you've entered your username and password. This helps prove that your you and that your account hasn't been compromised. For Office 365 desktop/mobile applications you only need to authenticate once unless you choose to logout of an application.
There are several methods for enabling 2FA. I prefer the mobile phone text code since it's convenient and it enables me to log into my account anywhere there's a browser. There are other methods available, but this tutorial uses the text message to a mobile phone option.
Step 1, after your regular login your presented with...
The first step is confirming your email address and is just a double-check that your information was entered correctly for the correct Microsoft account.
If everything looks correct select 'Next' to continue
Step 2, how do you want perform your verification...
You have several methods to authenticate. Use the first drop-down box to select your preferred method and fill in the rest of the information.
For our demo, I selected Phone, followed by 'United States' and then to send me a code to that mobile phone number. When your finished select 'Next'
Step 3, confirmation!
The final step is a confirmation. For my demo I was texted a 6 code and once entered correctly I was given access.