One of the greatest things about OneNote is its outlining capabilities. It's perhaps the most underrated feature as well as the one we most often take for granted. People often use outlining without even knowing they're using it.
What is outlining you ask? Well, Webster defines it as "a condensed treatment of a particular subject <an outline of world history>" or "a summary of a written work: synopsis: a preliminary account of a project."
In OneNote each note you take is an element of an outline. It might be a paragraph of text, or just a single list item. Each outline appears in a container, surrounded by a thin line and a grab-handle along the top edge.
To resize the outline just click the resize handle of the top border and begin dragging. Or you can click anywhere along the right border of the outline.
If you're making a list of items you plan to take with you on an upcoming camping trip. You might begin with something looking like this:
Each outline element has a small grab box on its outside edge. It's appearance conveys different meanings. For example, it might look like this, which means you can grab it and drag it around to rearrange the order or level, or even drag it outside of the outline. It only appears when you mouse over the element. Or it might look like this, which means it's currently a selected element. It might also look like this, which means it's in a collapsed state.
You can also drag-to-select, similar to selection in other Windows applications.
You can also right-click the grab box of a given element and choose Select All at Same Level. This will select all children at the given level.
Each outline is self-contained. This means that all formatting changes are contained only within itself. For example, you might decide to change the text style to a different font. Then when you click elsewhere on OneNote's page surface to begin a new outline, the font you selected previously won't be in effect.
This also holds true for bullets and numbering styles.
You can do this by right-clicking on the outline's grab-handle. Then you can select Order from the menu and choose Bring to Front, Send to Back, Bring Foreword or Send Backward.