In order to share your location to a private group, you must first be a member of or create a private group. If you have not done that, please follow the instructions in this article.
And if so,
1. Navigate to your private group where you should see a private group map.
2. Next, initiate a Share by tapping the 'G' icon at the bottom of the map
3. The Glympse configurator will appear. You will notice, however, that you cannot edit the recipient, as it will always be the group. Configure the rest, if desired: destination, duration and/or a message. Then tap Send.