You need to be Trust Level 1 in order to get an invite. Here are the requirements to reach that level -
Trust Level 1 Requirements
Then after you’ve reached Trust Level 1 open the “SAFE Browser” and access the Authenticator page by selecting either area circled in red as indicated in the image below:
Then on the page that loads select “CREATE ACCOUNT”. After you select “CREATE ACCOUNT” you will be guided through the process of creating an account and obtaining an invitation code.
Please let me know if you need any help with the create account portion.