Before you proceed, you need Spaces installed on your phone.
How to invite members to join a Space?
Step 1 - Open the Space wherein you want the users to join and Click on the three-lined menu icon located on the top right corner of the screen.
Step 2 - Select from the multiple sharing options: QR code, Forward, Share the link to join.
Note: When you want to moderate the incoming member request, to make sure the correct member is allowed to Space, you can choose to enable moderation and the Space connection request would be kept in pending state. The Owner/Admin would have to confirm the request & only after that the member can be a part of the Space. Have a look at this guide from more information Click here.
You are done!