Hi,

Please follow below the steps to add another email account on MSN.

1: Sign in to MSN software with the primary email address.

2: Go to Help and Settings and click on Accounts and Billing.

3: Select Add Member account and you will get the screen to select
   a) Create an MSN.com e-mail address for the new member
   b) Type an existing MSN or Hotmail e-mail address

4: If your creating new account, please select the first option and click on Continue where you have to fill in the form to generate a new email account.
  
5: If your adding existing email account, please select the second option and type in the email address which you would like to add and click on continue.
   In the next screen, it prompts to enter the code which is sent to the account which you are trying to add to verify the account and then click next.

Please contact MSN Technical support team incase if you find any issue while adding the email account.

Please check the private message for MSN Support number to get assistance

Note : Please sign in with your MSN email address and password to check the private message

Thanks

Jason