Now that you have a sub account setup, you can access your sub account from the member app.
There is also the ability for the sub account to access the Member App.
One main difference between a Primary Account and a Sub Account is the fact that Primary Accounts login using their email address and a password. Sub Accounts login using a username and a password.
To setup a Sub Account's username and pin, simply navigate to the Edit Person page for the Sub Account and enter the information here.
As with any account, you can simply set the username here and then click on the "Send Account Setup/Update Link" link on the right rail of the page.
Note: The username cannot be the email address of the Primary Account.