This is a child page of the About section. You can edit this page to add in your mission, or give it a new title and use it to add another subsection, such as Board or Staff or delete it entirely.
It has been given a menu link so that it will appear in the main menu (as a drop down link under About.) Menus can be edited and re-ordered at admin/structure/menu. Visit the documentation page to learn more about working with menus.