It doesn't come as a surprise that genealogic data forms a tree - a Family Tree. GenJ looks at the origin of that tree and displays all its ancestors and all its descendants. One exception though : only direct descendants with their spouses and direct ancestors with their spouses are shown. So the brother of your grandfather becomes visible after you make latter or any of his ancestors the origin of the tree.
You can browse the tree by scrolling and by selecting individuals or families. Everytime you select one of the entities the Edit View is notified to display it. By double-clicking on an entity you make it the origin of the tree. After a short recalculation the tree displays itself in the new layout. If you want to restrict the shown information you can remove sub-trees by clicking on the small minus (-) / plus (+) symbols attached to the family-child relationship line.
The toolbar at the lower/right offers additional functionality: