Two methods: Text message authentication or Microsoft Authenticator application. Requires a mobile device in both scenarios.
To choose which method you would like to use
1. Go to portal.office.com and sign in using your CTS email and password.
2. Click your initials or picture at the top right of the screen then click "My Account". It will bring you to a page that looks like 
3. Click "Security & Privacy" then click "Additional Security Verification".
4. Click "Update your phone numbers used for account security".
5. This will bring you to the multi-factor authentication page. Your page will most likely be blank.
From there, you can choose one of the two methods below.
Text Message Authentication:
1. In the drop down menu, select "Text Code to my Authentication Phone".
2. Make sure the option "Authentication Phone" is checked. Select the correct country code and input your mobile phone number that you want to receive text messages.
3. Skip "Alternate Authentication Phone" field unless there is a second phone that you would like to enter as a backup.
4. Click "Save".
5. If Microsoft prompts for a code to verify your phone number, they will text a 6 digit code to your phone. Input that number in the field and click "Next" or "Verify". Once that is done, open your Outlook.
6. On the first start up of Outlook, enter your CTS email and password. Microsoft will ask text you a different authentication code.
You will have an option that says "Remember this device for 30 days". Make sure that is checked otherwise you will need to enter a different authentication code every time you login to your email from that computer or phone.
Microsoft Authenticator Phone Application.
1. Go to your app store on your mobile device and download Microsoft Authenticator.
2. In the drop down menu, select either "Notify me through app" or "Use verification code from app or token".
2a. "Notify me through app" means that when you sign in from a new device, your phone will send you a push notification for you to either approve or deny the login.
2b. "Use verification code from app or token" means that when you sign in from a new device, you will need to enter in the 6 digit code from your phone application. Keep in mind that it is completely normal for the code to change every 30 seconds and the code won't be the same for each login.
3. Check the box that says "Authenticator app or Token". Then click "Set up Authenticator app". It will look like
4. Write down the code and use your phone to copy the URL link (really tedious if you try to write and then type the entire URL).
5. Go to your Microsoft Authenticator app -> click the 3 vertical dots at the top right of the screen -> Add Account -> Work or School Account -> click "Enter Code Manually" at the bottom and enter in the code and paste over the URL.
6. Skip "Alternate Authentication Phone" field unless there is a second phone that you would like to enter as a backup.
7. Click "Save"
8. Microsoft may ask to verify that your app is working correctly. If prompted, enter in the 6 digit code that is tied to your account.
9. On the first start up of Outlook, enter your CTS email and password. Microsoft will either ask you to approve or deny the login or ask you to enter a 6 digit code depending on which option you chose on step 2.
You will have an option that says "Remember this device for 30 days". Make sure that option is checked otherwise you will need to authenticate. every time you login to your email from that computer or phone.