Sub accounts are designed to help those clients who have more than one website and would like to activate Justuno on all of them. The major benefit of using sub accounts is that you have one login for all accounts, making it drastically easier to manage multiple Justuno accounts. Here is an article about embedding Justuno on multiple sites if you're not interested in sub accounts. The main reason users want to use a harder method like embedding Justuno on different sites instead of using sub accounts is that the billing will be on one account. Here is how billing works for sub accounts.
Step 1: Head to your settings wheel on the right hand corner of your dashboard next to your login name. Then hit "Sub account admin"
Step 2: Hit add new account
Step 3: Enter in your new accounts information. If you're an agency and are doing this for a client you have options to use their email address for the log in and who gets which notification emails. There is also the option to use the master accounts billing information!
Step 4: How to revert back to your "master account". Head to the same settings wheel and hit "Revert to Master".