The Jira agile board is able to work on either one specific project or multiple projects at once. When you want to have multiple projects, you will need to use filters to define what issues will be included. For this reason, understanding and being able to use Jira Query Language (JQL) effectively can be very handy. You can find more information on JQL at https://confluence.atlassian.com/jiracoreserver075/advanced-searching-935563511.html.