In Ubuntu, an application can be started by selecting its icon from the application list (triggered by clicking to the icon at the lower left corner or pressing window key).

This list of icons is stored in /usr/share/applications (for all users) and ~/.local/share/applications (for specific user). The icon is defined in .desktop file.

Icon/application's starting command can be easily figured out by looking at the associated .desktop file's content at the TryExec entry.