You can invite members from your team to the organisation card from the settings section of your organisation profile.
Navigate the Settings > Connections
Click "Invite your connections"
Add the email addresses of the people you want to invite
Click "Invite"
You can find all invited connections on the "Invited" tab. There you can also withdraw the invitation.
The person you invited will get an email invitation which they can use to register a user profile. After they have registered their user profile, you can choose whether to display them on the organisation card and if you want to extend them admin rights.
Display members on the organisation card
Click the pen icon that appears under the "display" column
Choose whether they should be shown as a team member or a contact person. Both are shown on the profile page of the organisation. If you leave this empty, this connection will not be visible on the organisation profile.
Contact person: Visitors can send the contact person a message.
Team member: Visitors can see the team member but not send them a message.
Admin permissions
The person who creates the organisation has automatically admin permission to it. As an admin they also control who else has admin permission to it. When a new team member has registered their profile, the admin can choose to extend the admin rights to them as well or keep it as it is.