You can invite someone to a space by sharing a link or sending them an invitation using their email address or name (if they have an account on Threads).
To invite someone to a space:
- Go to the space
- Click on Invite members on the right-side of the space
- Share a link to the space or invite people directly to it. You can also sign in with Google to import your contacts.
If you want to add someone directly to a thread but not to the space, you can add them as a guest.