To start a program, you have several options:
In the bottom panel, click Applications and select the desired program from the hierarchical menu.
Open the Activities Overview by pressing Meta. Now click an application icon or search for an application. If you do not know the exact application name, you can search for generic category names such as “image editor”.
If you know the exact command to start the program, you can press Alt–F2, enter the command into the dialog and press Enter.
Note that the only button displayed in the window is labeled Close and will indeed close the window.