Once the mailhost is configured users can register.
Open https://YOUR_INSTANCE_URL/erp5/web_site_module/default_wendelin_data_lake/ and on left side panel click on Register.
Note: Pay attention on / (slash) at the end of the url, it is mandatory.
Note: Registration works only if user is not logged in. Thus, before registering a new user make sure that you are not logged in with any user.
After filling the form and clicking on Register you will get an email to the specified email address with further instructions.