• WhatsApp is giving users three levels of group invite privacy options, which users can select by going to the Settings screen in the WhatsApp app and then tapping Account > Privacy > Groups. These three options include:
• Everyone: This option allows any WhatsApp user to add you to a group.
• My Contacts: This option lets anyone in your phone’s contacts add you to a group. If a WhatsApp user is not in your phone’s contacts, that user will not be able to add you to a group.
• My Contacts Except: This option will let anyone in your phone’s contacts add you to a group except for certain 
• If someone tries to add you to a group but you don't have one of the above permissions, the group admin will be prompted to send you a private WhatsApp message inviting you to join. You'll have 72 hours to accept the invite before it expires, according to WhatsApp.

Read More: How do I block a person from joining a WhatsApp group?