There are three visibility settings that you can adjust within Google Groups settings:

1. Who can see your group
2. Who can join your group
3. Who can see your group's conversations 

What these settings control:

• Google Group setting: Who can see your group

          

• • “Who can see groups” changes “who can find the page” for the group. If your group needs individuals to subscribe via the web page, they’ll need to be able to see the page. Enable this setting to allow non members to subscribe via the web page.

• Google Group setting: Who can join your group

• • “Who can join the group” defines “who can join the Google group”. 
    Your group may want “who can see the group” and “who can join the group” to be coordinated so individuals who want to join the group can also see the group. If individuals cannot see the group, they will only be able to subscribe via email.
    • Read about how to subscribe via email 

• Google Group setting: Who can see your group's conversations

• • “Who can view the group conversations” changes who can view the conversations of the Group. This is automatically coordinated with the the “who can join the group” setting so that anyone who is allowed to see the conversations can see the group but not necessarily everyone who can see the group can see the conversations.
  • A common user error occurs here when new members are trying to join a Google Group and cannot see the content. Adjusting this setting to “everyone” will resolve the content “error” you are seeing and allow people to see the conversations within the group. This is appropriate if the content of the conversations can be made public - to the organization and/or to external users.

Additional Resources:
Who Can See and Join Your Groups
Make It Easier to Find Your Group & Posts
Update a Group’s Settings