A user will have access to WordPress through their Kurtosys App user account. Thus, they will need to be added to the Kurtosys App as a user first, and then go to Site Management, choose the environment and then click the WordPress Admin button to go into the WordPress Admin area.
If a user is added as a SuperAdmin (WordPress user type), they will automatically have access to each site within the Network of subsites.
If however, the new user is not a SuperAdmin they will need to be added through a different process. This article explains this process.