You can create as many boards in your Account as you like, and each board can kept private, shared with specific people, or made available to the public to view. There are no limits to the number of boards that can be owned by any Account.
Each account is associated with a specific email address:
(And, yes, you can create more than one account if you like – although we wouldn't really recommend that – by using different email addresses to sign up.)
(Visitors don't count.)
Here's an example: you have three boards with some people working as Team Members and people viewing as Visitors.
(The Team Members are highlighted here in red squares, and the Visitors in circles.)
Everyone who is a Team Member, on any of your boards, is part of your Account Team. People who are part of your Account Team can create boards in your account; you will own these boards.
As Account Owner, you have ultimate authority over all boards that exist in your account:
When another Kerika user adds you to one of the boards as a Team Member, you become part of their Account Team, which means you can create new boards owned by these people.
So at any time you could be working on some boards that you own – and on some other boards that are owned by other people.