When you open an existing Virtual Machine or create a new one its property page is displayed. The upper part of the page displays virtual machine name, name of the configuration file with the path, and general VM settings: guest operating system type and version (regardless of it is installed or not), acceleration level, last modification date, and others. Those settings that may be changed are link-looked and if click on any of them the Configuration Editor will be opened on the appropriate page. (The name of the Virtual Machine is not linked to Configuration Editor, however it can be changed on the General Options tab.)
The Configuration Details part shows all devices connected to the Virtual Machine and their current options. To edit any device simply click device name. The Configuration Editor will open the tab corresponding to the device.

The Command Button panel in the bottom of the property page contains buttons for creating a new Virtual Machine, browsing hard disk for a Virtual Machine to open, editing Virtual Machine configuration, and also saving opened Virtual Machine configuration.
The property page remains available when guest OS is running. You may open it to check the VM configuration. However, the Command Button panel will be disabled.