I have an existing board that I have lots of cards in and I want to invite my organisation to be a member.
I can only see creating a new board for my organisation. How do I invite my organisation?
You can move your existing board into your organization:
Menu > Settings > Change Organization
... and then you can choose to make it visible to everyone in your organization
Menu > Settings > Permissions > Visibility: Organization
If you don't add the board to your organization, you can still invite members from your organization using Add Members...
Alternatively you can copy your own board to a new board in your organisation so that all the cards remain.
Copy Board
can be found in Board's Options.