Agile boards, backlog, and sprint configuration
A board is a view defined by a saved filter plus board configuration. The filter's JQL determines which issues can ever appear; the board's columns map statuses to columns, and any issue whose status is not mapped falls into an unmapped or no-column area. Scrum boards add a backlog and sprints; Kanban boards provide continuous flow with optional column constraints and WIP limits. Board settings also cover swimlanes (stories, assignees, epics, JQL queries), the estimation statistic (story points or original time estimate), and ranking, which is stored globally and influenced by the filter ordering.
Sprint mechanics: create a sprint in the backlog, start it, and complete it. On completion, incomplete issues move to the backlog or to the next sprint, and the sprint report records what happened; deleting a sprint returns its issues to the backlog without a report. Velocity derives from completed story points across closed sprints, so changing the estimation statistic changes the numbers.
Traps: an issue exists but is invisible on the board - check the filter JQL, the status-to-column mapping, and whether the issue type is excluded; changing a board filter changes the board's contents for everyone; a story points field must be on the edit screen and in the field configuration for users to set it; and columns are driven by status categories and status mapping, not by column names.
Rule of thumb: when a board looks wrong, diagnose in order - filter, sub-filter, column mapping, swimlane, then permissions.