Welcome to Android Central! You've created the additional Google accounts already on the web, right? They have to exist first before you can add them to your phone.
If you already have those additional Google accounts created on the web, then look at page 296 of the manual (look at the actual page numbers on the printed pages, not the PDF pages) for instructions on how to add an account.
It says this file does not exist. I still cannot figure out how to add a second gmail (that already exists) to my Galaxy S3. Why is this so hard?!