If you like to make the situation of your public group more specified, and make it as a private group you can simply convert it to a private one.
In iGap app you are able to have groups in public as well. As it is assumed in public groups, a community of users can come together in a group and chat with each other. But if you want to have a group in private and do not make any unknown member enter your friendly community, convert your public group to a private.
In iGap app, also you can have groups in private or public, but you can convert them private to public or vice versa and apply new possibilities. Remember, in order to have a public group, you have to create a private at first. Then by converting to a public one, and adding new and/or unknown members get familiar with more iGap users.
You can create new groups in iGap using the option New Group and control and administrate it easily. In both Web and Android version, you are able to have either private or public ones. It's possible to have a private group with your friends known to each other or a public group in order to make new friends and get acquainted with more people.