By default, when you create a new project, the agile board created will only include issues from the current project. This is usually fine if your project is self-contained. However, there might be cases where you have multiple projects that are related, or dependent on each other, and in order for you to get an overall picture, you need to have issues from all those projects shown on a single agile board.
The good news is, JIRA lets you do just this. One thing to understand here is, JIRA uses what is called a filter to define what issues will be included on the board. Filters are like saved search queries, and when a project is created, JIRA automatically creates a filter that includes all issues from the current project. This is why the default agile board created with the project will always display the project's issues only. Filters are discussed in Chapter 10, Searching, Reporting, and Analysis.
So for you to include issues from other projects on the agile board, all you need to do is update the filter the board is using: