Make sure your Google Apps domain administrator gives you the right privileges. See the "Grant permissions to view users in domain" section on the Configuring Google Apps page.
Once you've completed the above steps, you will be ready to load user accounts from Google. To do that with Primalogik, click on the Administration menu (on the top menu bar) and then go to "Users". On the Manage Users page, you will find the "Import from Google" button that will allow you to select the users to import.
Click on that button to browse the user accounts that you can load and select the ones you want to enable in Primalogik.
For more information about the integration with Google Apps please refer to Configuring integration with Google Apps.