To create a forum that is only accessible to you and your guests, please follow the following steps: SHELF -> Community tab -> Create Private Forum. You can add guests at the creation step and you can modify the guest list at the forum's page.
Here are some of the potential uses of a private forum.
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You can now subscribe to a forum by clicking on the subscribe link on the top right corner of the forum's page. All forums you have subscribed are shown under SHELF -> Community tab. The purpose of this feature is to help you keep track of the forums that interest you.
I hope you like it! Please comment and let me know what you like and dislike. There will be another two minor updates today.
*cheers*