When you are creating an event you will see the option to 'Connect with Facebook' at the bottom of the page. Once you're connected, an option to 'Create a Facebook event?' will exist. Simply check this box and your event will be exported to your Facebook Group or Fan Page, depending on your settings.
If you've already created an event, just go to the 'Edit Event' tab and find the same option at the bottom, tick the box and click 'Save'.
Once created, events will appear in your group's 'News and Annoucements' section on your home page, and under the 'News' feature tab, as well as on your Group or Page's Facebook wall.
N.B. Due to recent changes to the way Facebook allows external sites to integrate with their system, we have had to remove the ability to import events from Facebook into your group. Creating your event on GroupSpaces first will allow you to synchronize RSVPs across both platforms, so this is the recommended solution.