It is a tutorial for customizing your toolbar, which I know isn't what you need, but it also talks about what each tool is for. It says that bottom tool is for selecting Vector objects, which is primarly text. The reason you can't click on it is because you don't have any text or other vector objects on your page to select. You need another tool for selecting and resizing the rastor layers (papers, elements, etc) . Maybe this page can help you find the tool you need. I think you are going to find it nearer to the top of the toolbar.