The Report Tree Toolbar does not actually appear as a Toolbar but is dockable only on the left and right sides of the design workspace. The Report Tree is used to view the objects you have placed in your report design.  Selecting an object in the Report Tree will make it become the selection in the report layout.  You can rename objects (for easier use in formulas) by right-clicking over the name of the object, selecting Rename, and then typing in a new name.  Make sure you hit the ENTER key after renaming the object to ensure the new name is assigned.