Arranging outlines is a simple matter of drag and drop. As you drag outline items, indicators will show where the drop will take place.
Alternatively you can adjust the outline hierarchy using the [Tab] key: Select the outline(s) you wish to indent and press the [Tab] key. The outline will become the last child of the current sibling above it. If you hold down the option key while pressing [Tab] the outline will become the first child of the current sibling above it. If an outline is the first child in a group of siblings it will not be moved.