loadLayout() loads the layout XML for the layout handles
<admin_brandLogo_index> (the route name for this controller action). These handles can be defined in any XML files in
app/design/adminhtml/default/default/layout (i.e. in the theme, or its parent theme). From this merged XML it generates a hierarchy of blocks. It executes everything defined in these XML files: instantiates block objects, arranges them, calls actions on them.
renderLayout() calls the render method of the root block. Usually that's
toHtml() and the page block with a template like
1column.phtml, but it could be anything that is defined in the XML. This root block subsequently renders its children, if
getChildHtml() is called from the template. The result is the complete HTML that will be sent as response.