At the top of a development window, two toolbars are displayed by default. They are separated by
the address bar, which contains class and feature fields and buttons to select the current view. The standard toolbar is above the address bar, the project bar below it:

You can hide toolbars (or the address bar) by unselecting them in the Toolbars sub-menu of the View menu or in the context menu that you can get by right-clicking in the empty space on the right of the bars. If you want them to be displayed again, just select them in the Toolbars sub-menu of the View menu.
In the standard toolbar, you will find buttons to manage tools and windows or that are related to the editor.
Note: For both toolbars, it is possible to choose which buttons are displayed and which ones are not. See the Toolbars customization page for more information.