You can either drag and drop items, or use the Alt+Shift+Arrow (Windows) / Cmd+Shift+Arrow (Mac) shortcut combinations to move items.
To drag and drop bullets into place via the desktop and desktop browser apps, simply click and drag a bullet (or highlighted selection of multiple bullets) to another position on the screen. You can move the item(s) below other bullets... or below and then slightly to the right to indent the item(s).
To move items using the mobile apps, just tap on an item (when not in editing mode... i.e. no keyboard visible), then hold and drag to the new position.
Note: To exit editing mode on mobile, just scroll in the window or click the keyboard icon to collapse the keyboard.