A board is a space that houses tickets going through the same workflow.
For example, you might have a board for development tickets with workflow stages like To Do, Design, Development, QA, and Done, and another board for tickets representing larger-scale projects with stages like Research, Design, Development, Rollout, Impact Review, and Done.
When you create a board, it'll be prepopulated with a default sequence of stages. To edit a board's stages, exit Settings to your new board, then while viewing the board, click the ellipsis menu and choose Edit stages.
Learn more about editing a board's stages:
By default, everyone in your organization can read and write tickets on all boards. That makes it easy for teammates to collaborate without unnecessary friction.
You can restrict a user by making them a Guest. This limits their access to only some of your organization's boards. That can be useful for, say, a contractor, intern, or other temporary teammate.
To manage which boards a Guest user can access, visit Admin Settings | Boards, hover over the board's ellipsis menu, then choose Manage guests. You can add existing Guest users in your organization to the board or invite new ones by email address. They won't be able to read or write any boards except those you explicitly grant them access to.
Learn more about user roles: