The complete documentation for MuLab is available as a set of HTML pages.
Much of the information provided here is extracted from that manual.

Audio Setup

When you first open the application, you may need to set up the communication between the application and the audio driver for your computer’s sound card (audio interface hardware). If the Audio Setup window is not opened for you automatically, you can click on the MuLab button and choose Audio Setup from the menu.

On OSX, choose the Core Audio device driver for the built-in audio of your computer (or for another audio interface, if you have one). On Windows, choose an ASIO or MME device driver. On Windows it’s best to use the specific ASIO driver that comes with your sound device. If no such driver exists then you should try the free device-independent driver Asio4All. Please note that Asio4All is not a MuTools product, if you need support on Asio4All please go to the Asio4All website. If Asio4All isn’t working for you, then select Driver Type = MME Audio, Driver Name = Sound Mapper.

Menus

The menus in MuLab don’t appear in your computer’s main menubar. There are menus that pop up when you click on one of the two buttons labeled MULAB and SESSION, for access to global program settings and operations. However, most of MuLab’s functionality is accessed via the contextual menus that pop up when you right-click an object (control-click, on Macintosh). You can never do something wrong by right-clicking somewhere. On the contrary: try right-clicking every possible object on the screen and you may discover extra functionalities.